A convert that enters to join to [the] jewish people is obligated in circumcision. If he was already circumcised when he was a Idol worshipper or he was born circumcised (the Tur quoting the Rosh), its necessary to draw blood from it and not bless on it (the circumcision).And If the organ was destroyed , [the fact that] there isn't circumcision [does not prevent him] from converting and its enough for him [to convert] through immersion [alone]. [If] he immerses before he is circumcised, it is effective, that afther the fact he was immersed and there are those who say that he [the convert] doesn't have to immerse [due to the circumstances].
When a person comes to convert, say to him, "What did you see that motivated you to come to convert? If you know that Israel, in this time, that the Jewish people are oppressed, eroded, (The words are from "Why is your strong one overthrown?" -Jer. 46:15) insane, and suffering. If he says, I know this and I will still become a part of your people, receive him immediately and tell him the principles of the faith, that God is one and idol worship is forbidden, and tell him a lot about this, and teach him a few of the lighter mitzvot and a few of the more stringent mitzvot, and teach him about some of the punishments of the mitzvot, as it says, "Before you came to learn this, if you ate the forbidden fat, you would not be punished with excommunication, you transgressed Shabbat and you were not punished with stoning; but now, if you eat forbidden food, you will be punished with excommunication; and if you transgress Shabbat you will be punished with stoning." Don't say too much about this, and don't get too specific either. And when you teach him about the punishment of the mitzvot, also teach him about the rewards of the mitzvot and teach him that in the doing of certain mitzvot that will merit life in the world to come. There isn't a complete righteous person, rather a master of wisdom, that does the mitzvot and understands them. And say to him: "You should know that the world to come is hidden from the righteous, who are Israel. As for what you see that Israel is in distress in this world, because it is not granted them to receive the abundance of good things in this world like other peoples, lest their hearts should be indulged loftily and they should go astray and squander the reward of the world to come. But God didn't bring to them too much destruction, so that they would not observe. Rather, all of the idolators stand. And you explicate this idea so that he feels the dearness of it. If he receives this, circumcise him immediately and wait until he is fully healed, and afterwards, immerse him without a barrier. (Some say that you cut or shave his hair and you cut his fingernails and his toenails before immersion.) And three learned scholars stand at his back and teach him some of the light mitzvot and some of the more stringent mitzvot a second time, and he stands in the water. And if it is a woman, women sit her in the water up to her neck and the beit din is outside and they teach her some of the easy mitzvot and some of the more stringent mitzvot and she sits in the water and afterwards, she immerses before them and they turn their faces and leave in order that they do not see her when she is getting out of the water, and they bless the immersion after she comes out of the water. And once he has immersed, it is as if he is a Jew, but if he goes astray, he is like an apostate Jew - he is still sanctified, and his marriage is sanctified.
All matters of the convert from making known to them the mitzvot, receiving them, the circumcision and the immersion, it must be with three who are fitting to judge, and during the day. But after the fact if he only was circumcised or immersed at night or in front of [the convert’s] relatives [which is invalid], or even if one did not dunk with the intention of conversion, rather a man who dunked for a seminal emission, or a woman who dunked for menstruation, they are still converts and he is permitted to [marry] an Israelite woman. So this all applies to the immersion and the circumcision but it does not apply to receiving the mitzvot, which prevents [conversion] unless it was during the day and in front of three [witnesses]. However, the Rif and the Rambam [say that] even after the fact [one who] immersed or was circumcised before two [witnesses] or at night prevents [conversion], and [marrying] an Israelite woman is forbidden. But, if he is married to an Israelite woman and she has borne him a son, we do not invalidate him [the son].
Since the ritual of immersion of a convert needs a beis din of three, do not immerse him on Shabbat and not on yom tov and not during the night. But if he immerses [during these times], indeed this [individual] is a [proper] convert.
One who circumcises a convert blesses, “Blessed are You, Eternal our God, Ruler of the Universe, who sanctifies us with Your mitzvot and commands us to circumcise converts.” And afterwards bless, "Blessed are You, Eternal our God, Ruler of the Universe, who sanctifies us with Your mitzvot and commands us to circumcise converts and to draw from the blood of the covenant.” Were it not for the blood of the covenant the heaven and earth would not be able to stand, as it says “Were it not for my brit, day and night, I would not have placed the laws of heaven and earth.” (Jeremiah 33:25)
[If] a non-Jewish woman comes to convert and she is pregnant, her child does not need to be immersed [after the child is born].
A minor who is an idol worshipper, if he has a [living] father, the father can convert him [i.e. present him to be converted]. And if he does not have a father and he comes to convert, or if his mother brings him to convert, a beit din can convert him, because it’s a merit to him, and we can give a merit to [the child] outside of his presence [because he is a minor and has no legal capacity]. Whether he is a minor who is converted on behalf of his father, or whether he was converted by a beit din [in the absence of a father], when he is older he can protest his conversion - we don’t treat him the way we would treat an adult convert- he is not like an apostate Jew, rather like an idol worshipper.
And what is this talking about? [A converted minor] may not act in accordance with the practices of Israel until they become an adult; but as soon as one becomes an adult and acts in accordance with the practices of Israel, he can no longer protest [his conversion].
An idol worshipper who comes to cut his foreskin due to an affliction or due to boils that appears out of nowhere, it is forbidden for Israel to cut, because there is no intention towards it as a mitzvah. If, rather, the idol worshipper intends for this to be a circumcision, it is a mitzvah for Israel to circumcise him. (And there are some places in which it is allowed for one to heal the idol worshipper, then it is permitted in every circumstance. - Nivukei Yosef)
[One who was previously known to have been] a male or female non-Jew, who comes and says, “I was appropriately converted by a beit din of So-and-So," they still should not be believed to come to the congregation [get married] until the witnesses [of the beit din] come. But if you see them behaving in customs worthy in the way of Israel and they do all of the mitzvot, they are presumed to be righteous converts, in spite of the fact that there were no witnesses to bear witness about who converted them. And if this is the case, if they come to mix [marry] into Israel, do not marry them until the witnesses come, or until they are immersed before us, since they initially had a known status as idol worshippers. However, one [whose status was never known] who comes and says that she is an idol worshipper and was converted by a beit din, believe her, for the mouth that forbids [and admits, “I am an idol worshipper” when she didn’t have to] is the mouth that permits [and says “but I was converted by a beit din.”]. And the Rambam writes that this ruling only applied in former days, and even then, only in the land of Israel, but outside the land one needs to bring evidence before he can marry an Israelite - because [the Sages] enhanced the strictures when it came to lineages [in Jewish communities outside Israel].
A man who is presumed to be Jewish and says, "I converted myself, alone”: if he has children, his testimony is not believed about his children [to annul their Jewish status], but you do believe the father to confirm his own status as a "forbidden portion," and [by dint of his own admission] he becomes forbidden from marrying an Israelite woman until he is immersed before a beit din.
When a [potential] convert comes to convert check after him, perhaps it is because of money he took, or because of power she will gain, or because of fear that [the pontential convert] is coming to enter the religion. And if he is a man, check after him perhaps he placed his eyes on a Jewish woman. And if she is a woman, check after her perhaps she placed her eyes on the single men of Israel. And if you do not find to them [such] a cause, inform them of the weight of the yoke of the Torah, and the difficulty of fulfilling it on the nations of the world in order that [the potential converts] leave. If they accept and do not leave, and you see them that they are returning out of love, accept them. And if you did not check after him or you did not inform him of the rewards of the commandments and their punishments, and he was circumcised and immersed before three ordinary people, this is a convert. Even if you are informed that it is because of some thing (like those discussed above) that he converted, since he was circumcised and immersed he has left the category of Idol Worshippers (i.e. Non-Jews), and we are worried for him until his righteousness is clarified. And even if he returns and serves Idols, he is like an apostate Israelite that his marriages are marriages. [Rama]: An apostate Israelite that repents does not need to immerse. Just that rabbinically he should immerse and accept words of joining (strict observance) before three.