In scripture they show up in the book of Acts when there is a need of table waiters The church was made up of Hebrews and Hellenists- those who spoke Greek. It was over the feeding of the widows. The apostles decided that seven men full of the Holy Spirit were to be chosen for this task.
Today the Deacons are there to help the pastor of the church in areas of service such as serving communion, handling the money used for meeting needs of the people.
Paul thought this so important that he tells Timothy, a pastor of a church in Ephesus, the things to look for in choosing a man to be a Deacon. This is recorded in 1Timothy 3. Trustworthy, above reproach, not a drunk. The husband of one wife-- gentle not quarrelsome. not in it for the money, You can read it for yourself
They are very important people. Pastors work with deacons. Deacons serve the people. Pastors preach the word. Deacons free them up to do so.
In fact, you can do a study of deacons using a concordance and a Bible dictionary. Doing a word study on the term Deacon should be an interesting Bible Study for you.