The time is fulfilled, and the kingdom of God is at hand; repent and believe in the gospel.
And when Jesus came to the place, He looked up and said to him, “Zaccheus, hurry and come down, for I must stay at your house today.” So he hurried and came down and received Him joyfully….” And Zaccheus stood and said to the Lord, “Behold, Lord, the half of my goods I give to the poor. And if I have defrauded anyone of anything, I restore it fourfold.” And Jesus said to him, “Today salvation has come to this house.”
The first thing we must do to follow Jesus is to turn from our former way of life (repent) and trust in Jesus (believe). This is how you become a Christian. As Christians we are also to help others to repent and believe.