Albert Barnes Commentary Acts 13:5

"And when they were at Salamis, they proclaimed the word of God in the synagogues of the Jews: and they had also John as their attendant." — Acts 13:5 (ASV)

And when they were at Salamis. This was the principal city and seaport of Cyprus. It was situated on the southeast part of the island and was afterwards called Constantia.

In the synagogues of the Jews. Jews were living in all the countries adjacent to Judea, and in those countries they had synagogues. The apostles uniformly preached first to them.

And they had also John to their minister. John Mark, Acts 12:12. He was their attendant; he was with them as a companion, yet not pretending to be equal to them in office. They had been specifically designated to this work. He was with them as their friend and traveling companion, perhaps also employed in making the necessary arrangements for their comfort and for the supply of their needs in their travels.