What is the Mitzvah of sitting in the Sukkah? That he should eat, drink, sleep, lounge, (Tur) and reside in the Sukkah all seven days, both in the day and in the night, in the same manner in which he resides in his house the rest of year. And all seven days a man makes his house temporary and his Sukkah permanent. How so? The fine dishes and linens, should be in the Sukkah; and drinking vessels, such as glass cups and mugs, in the Sukkah; but eating vessels after eating (Tur), such as pots and plates, outside of the Sukkah. The lantern should be in the Sukkah. And if it was a small Sukkah, he puts the lantern outside the Sukkah. Rem"a: And he must not use the Sukkah for disrespectful things, so that the Mitzvot not be contemptible in his eyes. (Bet Yosef in the name of the Orchot Chayyim)
We eat and drink and sleep in the Sukkah all seven days, both day and night, and we do not sleep outside of the Sukkah, even a very short sleep. But one may eat an insubstantial meal outside of the Sukkah. And how much is an insubstantial meal? Approximately an egg's worth of a loaf of bread. And it is permitted to drink water and wine and eat fruit even if he made it his meal (own opinion) outside of the Sukkah. And he who is stringent upon himself, and will not drink even water outside of the Sukkah, he is praised. And a dish made of the five species [of grain], if he makes it his meal, it considered a proper meal and requires a Sukkah. Rem"a: And nowadays what is practiced to be lenient in the Sukkah, such that only the scrupulously observant sleep in the Sukkah; there are those who say that it is because of the cold, for it is uncomfortable to sleep in the cold places, and it seems to me that this is because the Mitzvah of Sukkah is a man and his household, a man and his wife, and in a place where he cannot sleep with his wife, that he does not have a suitable Sukkah, he is exempt; and it is good to be stringent, and to be there with his wife, just as he resides all year, if he can have a suitable Sukkah.
Eating in the Sukkah on the first night, is obligatory. If he ate an olive sized amount of bread, he has fulfilled his obligation. Henceforth it is optional; if he wished to eat a meal, he eats in the Sukkah; if he wishes, he can eat only fruits and nuts outside of the Sukkah all seven days, like the rules of eating Matzah on Pesach. Rem"a: And he should not eat on the first night until it is certainly night (Bet Yosef in the name of the Orchot Chayyim), and he should eat before midnight (Mahar"i Weill and Mahari"l); and he should not eat during the day from noon and onwards, so that he will eat in the Sukkah hungrily (Mahari"l), similar to eating Matzah.
All seven days, one recites Bible [and studies] in the Sukkah. When one is [trying to] understand [deeply] and be very careful with what one is reciting [and learning, one may study] outside of the Sukkah so that one is more focused. One may pray either in the Sukkah or outside of the Sukkah.
5. If it rains, one may go inside his house. From when is it permitted to go inside? From when so many drops of rain descend into the sukkah that, were they to fall into a cooked dish of beans which spoils quickly if only a small amount of water is added to it, that dish would spoil. RAMA: Even if he does not have a dish in front of him [Sma"g and Hagahos Ashiri]. A person who does not know how to calculate such a measure should reckon: If this same quantity of rain would come down into his house, he would leave his house, he may leave the sukkah. [Hagahos Ashiri; Mordechai; Mahari"l]. All of this applies specifically to the remaining days of the festival of Sukkot. But on the first night, one must eat an olive's worth in the sukkah even if it is raining [Tur; R"an; Rosh] and one must say Kiddush in the sukkah so he can pronounce the Zman regarding the sukkah
6. If one is eating in the Sukkah and it starts raining and he goes into his house and then the rain stops, he is not obligated to return to the sukkah until he finishes his meal.
7. If one is sleeping and it begins to rain at night, and one enters his house and the rain then stops, we do not bother him to return to the sukkah for the rest of that night. Rather, he should sleep in his house until dawn. RAMA: and then he wakes from his sleep (Tur). One who sleeps in the sukkah and it starts to rain does not have to wait the time that it takes for the dish to spoil, because even sleeping in light rain is unpleasant and he is allowed to leave. [Mahari"v] Whenever one is exempt from [the mitzvah] of sukkah, but does not leave the sukkah, he is not rewarded for dwelling there [at that time]. Instead, he is considered a commoner [Hagahos Maimoni]. When one leaves the sukkah because of rain, he should not leave brazenly, but submissively, like a servant who came to pour a drink for his master, and his master poured it out on his face, (as if to say, “I do not desire your service). (Mahari"l).
8. We are accustomed to only bless on the sukkah at the time of eating. (And this is how we [Ashkenazim] are accustomed.)