Where it started: Most believers in Jesus consider communion a sacrament, a practice that has been commanded by God that has a divine element to it. Communion can also be referred to as the Lord's Supper or the Eucharist. The tradition started during Passion week, the week before Jesus is crucified and is raised from the dead. Christ gathers with his disciples for the Last Supper, the same night he was betrayed and taken away for trial.
"As they were eating, Jesus took some break and blessed it. Then he broke it in pieces and gave it to the disciples, saying, 'Take this and eat it, for this is my body.' And he took a cup of wine and gave thanks to God for it. He gave it to them and said, 'Each of you drink from it, for this is my blood, which confirms the covenant between God and his people. It is poured out as a sacrifice to forgive the sins of many." (Matthew 26:26-27)
Why it continues: The apostles then teach followers of Jesus to practice the sacrament. Paul is writing the Corinthian church when he says:
"For I pass on to you what I received from the Lord himself. On the night he was betrayed, the Lord Jesus took some bread and gave thanks to God for it. Then he broke it in pieces and said, 'This is my body, which is given for you. Do this to remember me.' In the same way, he took the cup of wine after supper, saying, 'This cup is the new covenant between God and his people - an agreement confirmed with my blood. Do this to remember me as often as you drink it.' For every time you eat this bread and drink this cup, you are announcing the Lord's death until he comes again. So anyone who eats this bread or drinks this cup of the Lord unworthily is guilty of sinning against the body and blood of the Lord. That is why you should examine yourself before eating the bread and drinking the cup. For if you eat the bread or drink the cup without honoring the body of Christ, you are eating and drinking God's judgment upon yourself." (I Corinthians 11:23-29)
Communion reminds us of Jesus' sacrifice for the forgiveness of our sins. Paul also tells us it also symbolizes the new covenant. The old covenant bonds Yahweh and Jews, God's chosen people. The Old Testament informs Jews of how to reconcile themselves to God through sacrifices of animals and incense. In the New Testament Jesus is the "once and for all" sacrifice for all believers. Through Christ, the new covenant is available to Jews and gentiles (non-Jews) alike. When someone takes part in communion he/she is claiming to be part of the new covenant - Jesus reconciled he/she to God through His blood sacrifice on the cross.
How it's done: Communion is practiced for believers to remember. Jesus gave His life up in place of yours. It's not what you can do, it's what He has done. We cannot do anything to gain forgiveness; rather, we must accept the gift of grace. When practicing communion take time to remember why Jesus had to die in the first place. Examine yourself before the Lord and before you eat the bread and drink the cup confess your sins to God. Remember Jesus' betrayal, death, and the new life He gives you. He took your place because something had to be sacrificed to reconcile us to God. You are part of that new covenant now. Eat, drink, and thank the Lord.