Take a plate with one whole matzah (or one whole challah if performing the ceremony before Rosh Hashanah, Sukkot, Shemini Atzeret or Shavuot) and either a piece of cooked fish, cooked meat or a hard-boiled egg on it, (it is a good idea to wrap the matzah/ challah and fish, meat or egg in aluminum foil to easily keep them apart from the rest of the foods in your home). Recite the following blessing:

BA-RUCH A-TAH ADO-NAI E-LO-HE-NU ME-LECH HA-OLAM ASHER KID-E-SHA-NU BE-MITZ-VO-TAV VETZI-VA-NU AL MITZVAT ERUV.

Then recite: "By virtue of this Eruv, we (the members of this household), shall be permitted to cook, bake, keep food warm, carry, light candles and do all preparations on Yom Tov for Shabbat."

Put the foods you used for the Eruv away, and eat them on Shabbat. NOTE: The Eruv Tavshilin allows you to cook on Friday only for Shabbat, it does not allow you to cook from one day of the holiday to the next (ie: Thursday for Friday). It is permissible to cook only from a pre-existent flame, one that was lit before the onset of the Holiday on Wednesday before sunset.