The Pharisees and religious leaders wanted to kill Jesus but the problem was that they were constantly afraid to arrest him because of the crowds. Jesus had a lot of supporters towards the end of his ministry and they were afraid the people would stop them from taking Jesus. But at nights Jesus would go off away from the crowds with essentially just his disciples (the Twelve). How Judas betrayed him was that he told the Pharisees where they could find Jesus when he would be most vulnerable. He let them know when the crowds were gone so they could take him without resistance from the people.
Judas betrayed Jesus after accepting thirty silver coins from the chief priests and identifying Jesus to them with a kiss while Jesus and his disciples were in a place called Gethsemane. After Jesus was condemned, Judas was seized with remorse. He went to the chief priests and threw the thirty silver coins in the temple. Then he went away and hanged himself.
Drachma--- a Greek silver coin is worth about a day's wages. The temple tax was two drachmas.
Someone commented earlier that 30 pieces of silver was NOT a large amount, it was a trifle amount. I have to correct whoever said that. Since one silver is worth a day's wage, thirty silver coins will be worth about a month's earning.
In the Gospels that we have, Judas was one of Jesus's twelve disciples but envied him (or was possibly disillusioned because Jesus seemed to be uninterested in earthly revolution.) In exchange for thirty pieces of silver (a very large sum) he agreed to identify his leader in public, so that the Roman officers would know who to arrest. He did this by kissing him ("Judas kiss" was a common expression at one time.) Jesus was arrested and later crucified. He had foreseen that this would happen; he had also known that his most loyal follower, Peter, would deny friendship with him to save his own skin (this also happened.) Judas later hanged himself in remorse. In some countries, such as Greece, he is still burnt in effigy every Easter.
Quite recently a document known as the Gospel of Judas has been found, which claims that Judas was in fact a loyal supporter and the "betrayal" happened very differently. There is still a debate going on about this document.
