Q: Is it that the first day is considered Shabbat? Is only Friday at sundown to Saturday at sundown considered Shabbat?
A: "Shabbat" means Sabbath and it only refers to Friday sundown to Saturday after sundown when three stars come out (about 25 hours, actually). The first two days are a "yom tov" (literally "good day" but used to mean 'holiday'). Passover is a holiday, but it doesn't have the same limitations as the sabbath in terms of working, and of course one doesn't eat bread or some other foods during Passover.