Sacraments, it has been said, "effect what they signify." For Catholics, Orthodox and certain other churches and denominations, a sacramental life is central to Christian discipleship, and even Catholic canon law speaks of the "right" that Christians have to the celebration of the sacraments. We usually speak of the seven sacraments in terms of their overall function in the life of the church: sacraments of initiation are baptism, confirmation and eucharist; sacraments of reconciliation are reconciliation ("confession") and anointing of the sick; and the sacraments of vocation are matrimony and order.
Although we don't like to reduce things to pure functionality, we have to do that a little bit. It's important to remember, however, that there are usually three dimensions to ALL sacraments: they are OUTWARD signs, connected with Christ, that effectively communicate God's grace. The sacraments are always PUBLIC events; there is no such thing as a "private" sacrament.
Bishops may preside at all sacraments, including ordination of other ministers.
Presbyters preside over all sacraments, except ordination. While bishops are the original ministers of confirmation, presbyters may do so with proper delegation through canon law and the bishop.
Deacons preside over baptism and matrimony. Deacons do not confirm, do not preside over the Eucharist, do not hear confessions, do not anoint and do not ordain. Deacon do have, however, their own specific assisting roles in other sacraments, such as at the Eucharist or in anointing or at ordinations.
As ordained ministers, deacons also have other liturgical functions as well. Deacons are ordinary ministers of holy communion; deacons preside over communal celebrations of the Liturgy of the Hours, deacons preside at Benediction and may give the Eucharistic Benediction (lay persons may not), and deacons conduct wake services and funerals.
The role of the deacon, even while presiding, is to act in the person of Christ the Servant and in the name of the Church.