Nicolas was one of the seven men named in Acts 6:5 who was chosen to serve in the early Jerusalem church. His job, as specified in Acts 6:1–4, was to make sure food was distributed fairly and equally among all church members. People traditionally call these seven men "deacons" (which means "servers") because Acts 6:1 uses terms like "daily distribution" or "service" and 6:2 uses phrases like "to wait on tables" or "to serve."
Nicolas is the last name in the list. The Bible identifies him as a proselyte, which means he was a gentile (non-Jewish person) who had converted to Judaism before becoming a Christian. He had a Greek name, and his home city was Antioch. The New Testament does not give us any more information about him.