We have explained that there is a positive Torah commandment to recite Kiddush on the night of Shabbat. The Sages enacted that this Kiddush be recited on a cup of wine.
Everyone is equally obligated to recite Kiddush. Nevertheless, it is customary for the head of the household to recite the Kiddush aloud and have the rest of those present fulfill their obligation through the law that one who hears Kiddush is tantamount to having recited it. Thus, Maran Rabbeinu Ovadia Yosef zt”l writes (based on the words of Rabbeinu Shmuel Abohav in his Sefer Devar Shmuel) that when the individual reciting Kiddush reaches the name of Hashem in the Kiddush, those present should not reply by saying “Baruch Hu U’Varuch Shemo”, for one should not recite “Baruch Hu U’Varuch Shemo” while listening to any blessing one is likewise fulfilling one’s obligation through. The reason for this is because since the one listening to the blessing being recited is tantamount to reciting the blessing on his own, stopping to answer “Baruch Hu U’Varuch Shemo” after Hashem’s name is considered like one is interruption and adding unnecessary words into the middle of the blessing and as such, changing the appropriate text of the blessing established by our Sages.
Since all of those present fulfill their obligation through the recitation of the Kiddush by the head of the household, they must take care to hear the entire text of the Kiddush, from beginning to end, from the individual reciting the Kiddush. Those present must have in mind to fulfill their obligation by listening and the individual reciting Kiddush must likewise have in mind to have his listeners fulfill their obligation through his recital (as we have explained regarding reading Parashat Zachor and the Megillah on Purim).
It is forbidden to taste any food or beverage following sunset on Friday evening until one recites Kiddush. (If one accepts Shabbat earlier on Friday afternoon, it becomes forbidden for one to eat or drink immediately until one recites Kiddush although the sun has not yet set.)
Before Kiddush is recited, a tablecloth must be spread on the table on top of which two loaves of bread are placed and then these breads are covered with another cloth or napkin. This serves as a commemoration of the Manna that fell in the desert which resembled being placed in a box, for there was a layer of dew under it and over it while the Manna was in the middle. The Talmud Yerushalmi adds another reason for this which is that if the bread were uncovered and one opted to recite a blessing on the wine first as opposed to the bread, this is considered an affront to the bread (for its blessing is primary respective to wine). There are those maintain that if the bread is uncovered, one must actually recite Kiddush on the bread and not on the wine. Thus, one should make sure that the bread is covered before beginning to recite the Kiddush on a cup of wine.