Chabad

Shabbat is a day of rest that lasts from sundown on Friday evening through nightfall on Saturday night. In addition to a plethora of things that observant Jews will famously not do on Shabbat (such as driving, working, or turning on a light switch), there are a host of things we do do in order to “make the Shabbat a delight” (in the words of Isaiah 58:13).
A big part of the “delight” of Shabbat is the enjoyment of three Shabbat meals, mainly the first two—Friday night dinner and Shabbat lunch—that are elegantly prepared, preceded by the sipping of ceremonial kiddush wine and the breaking of traditional challah bread, and lingered over with songs, inspiring thoughts and camaraderie. (The third meal, eaten late on Shabbat afternoon, is normally lighter.)
If you are joining as a guest, the first thing for you to know is that guests are considered an integral part of any Shabbat meal. Your hosts are very happy to have you—their meal just would not feel right otherwise!