Holy Communion refers to the meal that Jesus instituted in the gospels in the New Testament. Other references can be found in 1 Corinthians 11:17-34.
There are two elements in Communion (also called the Lord's Supper). There is wine and bread. The wine represents the blood of Christ that was shed on the cross. The bread represents the flesh of Christ that was broken on the cross as well. Both show the sacrifice of Christ and the benefits of that sacrifice - the forgiveness of sins, the demonstration of the love of God, and the community of Christians past, present and future.
Christian theologians also say that the Communion is a sign and seal. It is a sign of the work of Christ (a visual reminder) and it is a seal of what God will do in the future - he will come again (according to the New Testament).
The big difference among Christians is whether the bread and wine actually turn into the body of Christ. Catholics believe this. They call this transubstantiation. Protestants do not believe this. They believe in more of symbolic understanding.
when i went school i saw people eat some bread and drink wine(but the teacher only drank wine)