The sacristy is the small room located near the sanctuary of the church. The sacristy often contains all of the tools, books, liturgical appointments, vestments, (and electronics) used in the celebration of the Sacraments.
Occasionally there is a separate work sacristy, which has a sink for trimming plants and janitorial supplies, as well as more storage. There may also be a vesting sacristy where the priest, deacon, and/or other liturgical ministers vest for the liturgies. These may contain a closet with the vestments and a work table for preparing the texts for the liturgy.
The Sacristan is essentially the steward of the sacristy. It is principally the role of the sacristan to prepare the liturgical books, to set out all the implements for the celebration of the Sacraments, and often to oversee the tidiness and order of the church interior. While it varies from parish to parish, it is the sacristan who usually provides a great resource to the clergy.