The role of altar server is integral to the normal celebration of the Mass. At least one server should be present to assist the priest.
Servers carry the cross, the processional candles, hold the book for the priest celebrant when he is not at the altar, carry the incense and censer, present the bread, wine, and water to the priest during the preparation of the gifts or assist him when he receives the gifts from the people, wash the hands of the priest, assist the priest celebrant and deacon as necessary.
Servers should receive proper formation before they begin serving at Mass. The formation includes instruction on the Mass and its parts and their meanings, the various objects used in the Liturgy (their names and use), and the various functions of the server during the Mass and other Litrugical celebrations.