Where did Paul spend the three years before he first went to Jerusalem?
The three years were spent in Arabia before the first Jerusalem visit. After a three-year stint, likely down in Arabia, he finally went up to Jerusalem for the first time to meet Peter face to face. This was before that initial Jerusalem visit.
Les explains that after a three-year stint—which he thinks was down at Arabia—Paul finally gets up to Jerusalem for the first time. There he is going to meet the Apostle Peter face to face. Les imagines that was quite a meeting because the two men came from totally different backgrounds. The surrounding context also notes that the Lord Jesus had referred to Paul face to face and appeared to him, and these things contributed to his constant pushing forward against all opposition.