On Yom Tov, one is permitted to prepare food for that day, however not for the following day. If the following day is Shabbos, one is permitted to prepare food on Friday for Shabbos, as long as an Eruv Tavshilin was made before Yom Tov. The procedure is as follows. On Erev Yom Tov (Wednesday or Thursday), the head of the household, should set aside a baked item such as bread or Matzah, and a cooked item such as meat, fish, or eggs (i.e. a food that is eaten along with bread). Each item should be at least the size of one Kezayis, preferably the size of one Beitzah. He or she should then recite the blessing of עַל מִצְוַת עֵרוּב and then recite בַּהֲדֵין עירובא. The foods for the Eruv should be set aside and may be eaten on Shabbos. Click Here to download a Bracha Card.