There are some people who may get confused with deacons and priests. They assume that these titles are the same. Deacons can assist priests when priests are conducting the Holy Sacraments. For example, the priest may officiate the mass and the deacon will be in charge of helping the priest prepare the bread and wine.
If in case there are some church celebrations that do not involve the mass, that is the time when deacons can only preside. The deacon can also be the witness during the sacrament of Matrimony while the priest will be in charge of giving the blessing of God to the couple who wish to be bonded by their faith and love.