Translation:Shulchan Aruch/Orach Chaim/274

The Laws Pertaining to Breaking Bread on Shabbos, 4 Seifim: 1. Every person is obligated to break bread on two [whole] loaves. One holds them both in his hands and breaks the bottom one. RAMA: Specifically on the night of Shabbat. However on Shabbat day, or on the night of Yom Tov, we break the top one [Kol Bo; Hagahos Maimoni] and the reason is according to the Kabbalah.

2. It is a mitzvah on Shabbat to break a big piece that will last you through the whole meal [and see above Siman 167].

3. Those participating in the meal may not partake [of the bread] until the person breaking bread [first] partakes [of the bread that he cuts]. If, however, two loaves are placed before each one of them, they may partake of their bread even though he has not yet partaken of his.

4. This meal, and the meal of the daytime, cannot be done without bread.