What does Paul mean that immediately he conferred not with flesh and blood?
Paul means he did not consult other people—especially the Twelve apostles—for authority or directions. Instead of returning to Jerusalem to seek Peter, James, and John, men who had been with Jesus, he received his direction from God rather than from human counsel. 'Flesh and blood' stands for consulting people.
Les explains that immediately after Saul of Tarsus was outside Damascus, he did not confer with flesh and blood. Human reasoning would have sent him back to Jerusalem to look up Peter, James, and John, the men who had been with Jesus for three years and headed the group he had been trying to destroy. But he did not consult those twelve men or pour out his heart to them. All God had said was that he would suffer for His name, and he had no explicit instructions yet about where to go. So the phrase means Paul did not seek human counsel or apostolic authorization; he did not go to the Jerusalem apostles, even though that seemed the common-sense thing to do.
To reveal his Son in me, that I might preach him among the heathen; immediately I conferred not with flesh and blood: