The server's role is to assist the priest at the Table in preparing for the Eucharist (Holy Communion) and in clearing the Table afterward.
The server also "processes the cross" at the head of the choir. A person undertaking this part of the role is called the crucifer. The role of server is an important role in creating a sacred space for worshippers and in assisting the priest in the central piece of the service- the Eucharist.