(1) On the second night of Pesach, we begin counting the Omer.¹Since this is a mitzvah, that is done only at a certain, specific time, women are exempt from counting the Omer. Magein Avraham says that women have since accepted this mitzvah as an obligation, but Mishnah Berurah says that in our areas, women are not accustomed to count the Omer. He quotes from Shulchan Shlomo that women certainly should not say the berachah. (Mishnah Berurah 489:3) You should stand during the counting.²You should also stand for the berachah. If, however, you did count while sitting, you have still fulfilled your obligation (and you need not count over again). (Ibid. 489:6) The mitzvah requires that the Omer be counted, as soon as possible after nightfall,³Counting the Omer is done after the Maariv prayer, before saying Aleinu. Later Poskim rule, however, once the stars have appeared, the Omer may be counted even before Maariv. (Ibid. 489:2,18) after (three medium-size star) stars begin to appear. If you did not count at the beginning of the evening, you may count the entire night. In the synagogue, on the eve of Shabbos and Yom Tov, we count after the Kiddush is said, in order to give precedence to the (proclamation of the) holiness of the day.⁴At home, however, we must count the Omer before Kiddush, as it is forbidden to eat before counting the Omer. (Ibid. 489:39) At the conclusion of Shabbos and Yom Tov, we count before the Havdalah is said, in order to delay the end of the day. If the last day of Yom Tov occurs on Shabbos night, when the Kiddush and the Havdalah are said over one [the same] cup of wine, we also count before, in order to postpone the Havdalah.

(2) If you forgot to count during the night, you should count during the daytime, but without a berachah. On subsequent nights, you may count with a berachah. If you neglected to count an entire day, you should count on all subsequent nights, without saying the berachah.⁵This law also applies, if you realized you counted the wrong Sefirah yesterday. (Ibid. 489:35) If you are not sure whether or not you counted that night, even though you did not count on the following day, nevertheless, you may count the remaining days with a berachah.

(3) If someone asks you, during twilight or later, "What is tonight's count?" You should tell him, "Yesterday was such-and-such," for if you would tell him today's count, you are not permitted to say the berachah, when you count the Omer later that night.⁶However, if, for example, you just said the number twelve, without saying today is the twelfth day, you can still count the Omer with a berachah. (Ibid. 489:22)

(4) Before saying the berachah, you should know what the berachah is for; that is, you should know the exact number of days of the Omer.⁷The later Poskim rule that it is permitted to count the Omer in any language you understand. If you do not understand, and, thus, you do not know what you are counting, you cannot fulfill your obligation, even if you count in Hebrew. (Ibid. 489:11) However, if you did not know it, and began the berachah with the intention of counting the number you will hear from your neighbor, you have also fulfilled your obligation. Similarly if you say the berachah with the intention of counting four days, but after completing the berachah, you realize that you should have counted five days, you should count five [days], and need not repeat the berachah. Similarly, if you made an error in counting, for example you should have said "six days," but you said "five days," if you realize it immediately,⁸Toch kedei dibur i.e., within the time it takes to say these three words, sholom olecha Rebbe (Peace be with you Rebbe). you should count the correct number, and you need not repeat the berachah; but if you made a short pause, you must repeat the berachah.

(5) When the first night of the Yom Tov occurs on Shabbos, ma'aravis are omitted,⁹Ma’aravis are poetic compositions that are inserted in the Ma’ariv service of Yom Tov. and, on the second night of Yom Tov, we say the ma'aravis of the first night. On Pesach, however, even if the first night occurs on Shabbos, nevertheless, on the second night we say the ma'aravis pertaining to that night, because it deals with the harvesting of the Omer which took place on that night.

(6) During [the first] thirty-three days of the Sefirah period (the counting of the Omer), the disciples of Rabbi Akiva perished. Therefore, it is the custom during these days to observe a partial state of mourning:¹⁰Should the need arise, it is permitted to say the berachah, שֶׁהֶתֱיָנוּ (shehechiyanu) during these days. (Ibid. 493:2) Marriages should not be performed and you should not take a haircut (or shave).¹¹Those that are permitted to shave on Chol Hamoed, are also permitted to shave during Sefirah. (See Kitzur Shulchan Aruch 104:11) (Ibid. 493:1) There are various customs regarding (the day on which to begin) to count these thirty-three days. Some communities have the custom of counting them beginning with the first day of the Omer, and, therefore, they forbid [weddings and haircuts] until Lag ba'omer (the 33rd day of the Omer). But when Rosh Chodesh Iyar occurs on Shabbos, which has two levels of kedushah (sanctity), the kedushah of Shabbos and the kedushah of Rosh Chodesh, they permit marriages and haircuts on erev Shabbos. On Lag ba'omer and from that day on, the restrictions are permitted, because on Lag ba'omer [Rabbi Akiva's disciples] ceased to die. We, therefore, rejoice somewhat, and we do not say Tachanun on that day. Although on that very day some of them died (mourning need not be observed for a full day), for the Halachah states, a part of a day is considered as a full day; therefore, you should not take a haircut, nor should weddings be held; until after dawn (of Lag ba'omer), but not in the evening. But if Lag ba'omer occurs on Sunday, you may take a haircut on the preceding erev Shabbos, in honor of Shabbos.

(7) In other communities, they permit (weddings and haircuts) until Rosh Chodesh Iyar, inclusive, which adds up to sixteen days. This leaves thirty-three days, during which these things are forbidden, [that is] until Shavuos, (but they permit haircuts on erev Shavuos). Nevertheless, on Lag ba'omer they permit (weddings and haircuts); (and if Lag ba'omer occurs on Sunday, they permit them on erev Shabbos, as I have written above.) In still other communities, they permit (these things) until Rosh Chodesh Iyar, exclusive of that day, and on the first day of Rosh Chodesh, the restrictions begin to apply. On the first of the three days of Hagbalah [the three days preceding Shavuos,] which is the thirty-third day (of the period the restrictions are in effect), they apply the rule, "A part of day is considered as a full day," and they, therefore, permit marriages and haircuts during these three days, as well as on Lag ba'omer, (as I have written above). It is essential that the entire community follow the same custom, and not that some follow one custom and others follow a different custom.

(8) The Sandak, (the person who holds the infant during the bris circumcision), the mohel, and the father of the infant, are permitted to take a haircut (and shave) on the day before the bris, towards evening, before going to the synagogue.¹²If the bris (circumcision) will be held on Shabbos, they are permitted to take a haircut or shave on Friday, even before midday. (Ibid. 493:13)

(9) Engagement parties, even with a meal, are permitted during all the Sefirah days; but dancing is forbidden.

(10) It is the custom that no work is performed, by either men or women during the Sefirah days, from sunset, until after the counting of the Omer. There is an allusion for this (in the Torah), because it is said, "Seven weeks" (Leviticus 23:15). [The word shabbasos, meaning weeks,] is derived from shevos, denoting rest, indicating that during the time we count the Omer, that is from sunset on, you should rest [refrain] from doing any work, until after you have counted the Omer.

(11) On the first night of Shavuos, the Maariv service is delayed, until the stars come out, for, if we would hold the service before this time, and usher in the Yom Tov, a bit of time will be lacking from the forty-nine days of the Sefirah, and the Torah says, "They shall be seven complete weeks" (Leviticus 23:15).