Paul may have described himself as a "Hebrew of Hebrews" and a Pharisee before he believed (e.g., Phil. 3:5; 2 Cor. 11:22), probably meaning that he spoke Aramaic as a first language. But we learn from Acts that he was born in Tarsus (Acts 22:3), in the Diaspora, among those Jews scattered throughout the world. Accordingly, Greek was also a first language for him.
We also learn from Acts that he was a Roman citizen (e.g., Acts 16:37), which probably meant that he came from a family of some wealth. He speaks of working with his hands as a step down for the sake of the gospel (e.g., 1 Cor. 4:12). He might have worked with leather and tent making in the mission field, but back home in Tarsus he more likely was the boss.
These elements in his background no doubt helped equip him to be the formidable apostle that he turned out to be. Paul was not one of the twelve apostles. For example, he did not fit the list of qualifications for Judas Iscariot's replacement in Acts 1:21-22. He had not followed Jesus from the time of John the Baptist.
However, he considered himself an apostle of equal status to the other apostles (cf. 2 Cor. 12:11). "Am I not an apostle? Have I not seen Jesus our Lord?" he told the Corinthians (1 Cor. 9:1). An apostle is someone sent on an official mission representing a greater authority. Paul received this commission, this role as ambassador, from Jesus himself. Jesus appeared to him and sent him to be a witness of the good news that Jesus is king (cf. 1 Cor. 15:1-8).
Paul would eventually understand his specific mission as apostle to the Gentiles, to non-Jews (e.g., Gal. 2:7). Acts regularly shows Paul going first to the Jewish synagogue when he entered a new city, but we know from Paul's own writings that the Jews in these synagogues were never his primary target (Rom. 15:16). He also felt led to places where the good news about Jesus' kingdom had not yet taken hold. For this reason, he never planned to spend long in Rome, because faith in Jesus was already well established there (Rom. 15:20).
It is hard to know exactly when Paul fully understood the nature of his calling, even though in hindsight Paul clearly understood this to be God's purpose for him from the start (cf. Acts 22:21; 26:17). It is possible it was very early indeed. He says that after Christ revealed himself to him, he went to the Nabatean kingdom of Arabia even before he returned to Jerusalem (cf. Gal. 1:17). Since he apparently stirred up controversy while he was there (cf. 2 Cor. 11:32-33), it seems likely that he was preaching to Gentiles from the very beginning.
Paul tells us it was about three years after he believed that he finally went back to Jerusalem (Gal. 1:18). Both Paul and Acts tell us he then spent about ten years thereafter back around his home city of Tarsus (Gal. 1:21; Acts 9:30). We can presume that he was preaching the good news during these years, even though we know very little about them. At some point, he became part of the exciting developments at the church of Antioch in Syria (cf. Acts 11:19-30)...