1. The Laws of Eruv Tavshilin, 24 Seifim: If a holiday falls on Friday, one should not cook something for Shabbat in its own pot. One can cook many pots for the holiday and if he makes too much, the leftovers are for Shabbat. Using an eruv, one can cook for Shabbat. (Meaning that the point of the eruv is so that one can cook and bake on a holiday for Shabbat along with what was already baked or cooked for Shabbat before the holiday, so that he is not starting the work on the holiday but is just finishing it.) Rem"a: It is permitted to make the eruv even at twilight (Mordechai at the end of Chapter "Bameh Madlikin").
2. This eruv consists of bread and a cooked item. If one only made it using a cooked item, it is permitted.
3. The measure of this cooked item must be a kezayit (olive's weight), whether [the eruv] is for one person or for a thousand, at all points of its existence. Rem"a: Some require the bread to be a kebeitzah (egg's weight) (Yerushalmi) and such is the practice, initially.
4. The cooked item must be something that accompanies bread - not barley.
5. The cooked item can be roasted, stewed, pickled or smoked. It can even be the small fish that are prepared by putting them in hot water and this is how they are cooked - one can rely on them. It can be cooked apples (the same goes for other cooked fruits) or small fish that were boiled.
One can rely upon lentils that are at the bottom of the pot before the holiday, or fat stuck to the knife that is scraped off, as long as it is a kezayit (olive's worth).
7. It is a mitzvah for everyone to make an eruv. It is incumbent on the leader of the city to make an eruv for his townspeople so that those who forgot to make an eruv, those who were forced not to, and those who made an eruv and lost it can rely on his. (This is also the case for ignoramuses who do not know who to make an eruv) (Or Zarua). However, one who can make an eruv and didn't make an eruv but rather wanted to depend on the leader's eruv is called a sinner and cannot rely on it.
8. When one makes an eruv for others, he need not specify (that). Rather, he can make it generally for all the residents of the town, and all who live within the techum (boundaries) of the town can rely on it. Rem"a: However, somebody outside of the techum cannot rely on it, even if he made an eruv techumin and can enter [the town], unless the maker of the eruv mentioned him explicitly (the Magid chapter 6).
9. The maker of the eruv must intend to exempt others, but he who is the beneficiary of the eruv does not need to intend such when the eruv is made. He [the eruv maker] should tell him on the holiday before starting to cook for Shabbat. Rem"a: If the leader generally makes an eruv for everybody, we rely on it by default (Ra"n chapter 2).
10. One who makes an eruv for others must transfer possession to them using a [symbolic] person. And everybody who can be used for a Shabbat eruv can be used for an eruv tavshilin, and everybody who cannot be used for that eruv cannot be used for this eruv. (And see above chapter 366).
11. The one who receives the eruv must lift it off of the ground a tefach (a handsbreath).
[The maker of the eruv] then takes the eruv from he who received it and blesses "...on the commandment of eruv." He then says "With this it will be permitted to bake, cook, insulate, light lamps, and do all that is needed for Shabbat on the holiday, for us and for X and for Y" or "for all the residents of this city." Rem"a: And one who doesn't know the holy language can say it in the vernacular that he understands (the Mahari"l).
Even with an eruv, one cannot cook on the first day of the holiday for Shabbat.
14. If one made the eruv with the intention of relying on it as long as it exists, even on a different holiday, he should initially not rely on it on a different holiday, but after the fact, he can rely on it.
15. If the eruv was eaten or lost before one cooked for Shabbat, he cannot cook unless a kezayit (olive's weight) remains.
16. After preparing for Shabbat, he can eat it.
17. If one started making dough and then the eruv was eaten, he can finish that dough. It is also the case that if one started to cook, he can finish the dish he started.
If one baked but did not cook or cooked but did not bake and then the eruv was eaten or lost, what he legally made, even if it was intended for the holiday, can be left for Shabbat. He can then cook more food for the holiday.
19. One who didn't make an eruv is allowed to light the Shabbat candle. There are some who forbid this.
20. If one did not make an eruv, just as it is forbidden for him to cook for himself, it is also forbidden for him to cook for others, even in their houses. Others are also forbidden to cook for him. The only solution is for him to give his flour and cooked things as a gift to others with an eruv. They can then bake and cook and give it to him. They can even cook in his house. If there are no others with an eruv, some say that he is permitted to minimally bake one loaf, cook one dish, and light one candle. Rem"a: If he made an eruv but did not specify the labors explicitly, just saying "With this it will be permitted for us to do all needed things," he is like somebody who made no eruv (Or Zarua). Somebody fasting on a holiday is forbidden to cook for others even for that day, because he is likened to somebody who made no eruv and is forbidden to cook for others (Maharil).
21. If one realized that he did not make an eruv before the morning meal, he can cook a lot in one pot and the leftovers will be for Shabbat. Rem"a: He can also go during the day into a room with a lit candle to look for something and leave it lit until night (Tur). There are some who permit even cooking in many pots, because it is before eating. This only holds when one eats from each one [that day].
22. If one realized that he didn't make an eruv on the first day of the holiday and it is Rosh Hashana, he cannot make an eruv on condition. However, if it is a Diasporean holiday, he can make an eruv on a condition: If today is holy, I do not need an eruv, and if today is a weekday, with this eruv it will be permitted for us to bake and cook... The next day, he need not say anything. Some say that if he doesn't have anything that was cooked yesterday, his condition does not work.
23. If one sinned intentionally (or unintentionally) and cooked many dishes not for the sake of the holiday, he can eat them on Shabbat or a weekday.
24. If one tried to circumvent the law by cooking two dishes for today and leaving one leftover for tomorrow, he is forbidden to eat it.