The greatest among you must be your servant.
Altar Servers are very important to Liturgy. They set up for the Mass, therefore need to arrive at least 20 minutes before Mass begins. They check with the priest for any special instructions.
During Mass and other liturgies, they assist the priest, helping the Mass flow smoothly. Altar Servers lead the responses during the Mass. After Mass, they bring all utensils/vessels to the sacristy for cleaning.