 From who? From, well, Peter and James, Jesus' relative. He talks about this in his letter to the Galatians, chapter 1, when he traveled to Jerusalem to learn from the apostles, people who knew Jesus on earth in the flesh. Paul never met Jesus on earth that we know of, unless he bumped into him at a feast in Jerusalem. He met him after Jesus had already ascended into heaven. He had that vision on the Damascus Road where Jesus appeared to him.