John the Baptist saw for himself but didn't keep it to himself. When he saw Jesus the next day, he told two of his followers who were with him. Jesus spoke to them directly inviting them to come. They did.
One of them, Andrew, then sought out his brother Simon Peter and told them they had found the Messiah.
The pattern of discipleship continues through the Gospel of John as each new disciple will go and finds someone else (I've been reading O'Day and Hylen's commentary on John.)
Excursus: Jesus is given several titles in this section, John 1:29-42--John calls him "the Lamb of God" in verse 29 and 36 and "Son of God" in verse 34; John's disciples call him "Rabbi" in verse 38; Andrew, "Messiah" in verse 41.