en_tn/act/13/05.md

city of Salamis

The city of Salamis was on Cyprus Island.

proclaimed the word of God

"Word of God" here is a synecdoche for "message of God." AT: "proclaimed the message of God" (See: rc://en/ta/man/translate/figs-synecdoche)

synagogues of the Jews

Possible meanings are that 1) "there were multiple Jewish synagogues in the city of Salamis where Barnabas and Saul preached" or 2) "Barnabas and Saul started at the synagogue at Salamis and continued to preach in all the synagogues they found while they traveled around the Island of Cyprus."

They also had John Mark as their assistant

"John Mark went with them and was helping them"

assistant

"helper"