Deacons are helpers. They provide practical assistance to Church members and help the Church body grow.
General references
And in those days, when the number of the disciples was multiplied, there arose a murmuring of the Grecians against the Hebrews, because their widows were neglected in the daily ministration.
2 Then the twelve called the multitude of the disciples unto them, and said, It is not reason that we should leave the word of God, and serve tables.
3 Wherefore, brethren, look ye out among you seven men of honest report, full of the Holy Ghost and wisdom, whom we may appoint over this business.
4 But we will give ourselves continually to prayer, and to the ministry of the word.
5 And the saying pleased the whole multitude: and they chose Stephen, a man full of faith and of the Holy Ghost, and Philip, and Prochorus, and Nicanor, and Timon, and Parmenas, and Nicolas a proselyte of Antioch:
6 Whom they set before the apostles: and when they had prayed, they laid their hands on them. (Act 6:1-6 KJV)
Or ministry, let us wait on our ministering: or he that teacheth, on teaching; (Rom 12:7 KJV)
Paul and Timotheus, the servants of Jesus Christ, to all the saints in Christ Jesus which are at Philippi, with the bishops and deacons: (Phi 1:1 KJV)
8 Likewise must the deacons be grave, not doubletongued, not given to much wine, not greedy of filthy lucre;
9 Holding the mystery of the faith in a pure conscience.
10 And let these also first be proved; then let them use the office of a deacon, being found blameless.
11 Even so must their wives be grave, not slanderers, sober, faithful in all things.
12 Let the deacons be the husbands of one wife, ruling their children and their own houses well.
13 For they that have used the office of a deacon well purchase to themselves a good degree, and great boldness in the faith which is in Christ Jesus. (1Ti 3:8-13 KJV)
If any man speak, let him speak as the oracles of God; if any man minister, let him do it as of the ability which God giveth: that God in all things may be glorified through Jesus Christ, to whom be praise and dominion for ever and ever. Amen. (1Pe 4:11 KJV)
Specific examples
The Seven Deacons
And the saying pleased the whole multitude: and they chose Stephen, a man full of faith and of the Holy Ghost, and Philip, and Prochorus, and Nicanor, and Timon, and Parmenas, and Nicolas a proselyte of Antioch: (Act 6:5 KJV)
Phoebe
I commend unto you Phebe our sister, which is a servant of the church which is at Cenchrea:
2 That ye receive her in the Lord, as becometh saints, and that ye assist her in whatsoever business she hath need of you: for she hath been a succourer of many, and of myself also. (Rom 16:1-2 KJV)