1. Which activities does the eiruv permit?
All activities that are permitted on Yom Tov -- e.g. cooking, grinding and sorting, as well as washing dishes and lighting candles. Activities that are forbidden on Yom Tov do not become permitted due to the eiruv, such as turning on lights.
2. Who has to make an eiruv tavshilin?
Usually, every individual is obligated in this mitzvah. In practice, when the head of the household makes an eiruv, all the family members are included.
3. Who does not require an eiruv tavshilin?
A person who does not intend making any preparations on Friday for Shabbat, and does not need to kindle Shabbat lights. A person who needs only to kindle Shabbat lights, should make an eiruv without a blessing. This may be relevant for a person who is staying in a hotel or is invited out for all the Shabbat meals.
4. Is a visitor included in the host's eiruv?
No. Therefore, he must make his own eiruv if he intends to do some Shabbat preparations on Friday. Alternatively, he can become a partner in the family's eiruv by acquiring a share in the food.
DESIGNATING THE EIRUV
5. Which blessing is recited upon making the eiruv tavshilin?
While standing, and holding the food in the right hand, say:
Baruch ata Ado-noi Elo-heinu melech ha-olam, Asher kid-shanu bi-mitzvo-tav, Vi-tzee-vanu al mitzvat eiruv. Blessed are You, the Lord our God, King of the universe, Who sanctified us with His commandments, and commanded us in the mitzvah of eiruv.
6. Is anything else said?
Yes. Following the blessing, a declaration must be made describing the purpose of the eiruv foods. This declaration is traditionally said in Aramaic, but it must be said in a language that one understands. So if one does not understand the Aramaic words, he should say the following translation:
By means of these eiruv foods, we will be permitted to bake, cook, keep foods warm, light candles, carry, and do all that we need on Yom Tov for Shabbat.
7. Should the eiruv foods be held when reciting the blessing and eiruv declaration?
Yes. If you forgot to hold the foods, you should pick up the foods and repeat the declaration, but not the blessing.