Bishops assist the Roman Pontiff in exercising his office. They are able to render him cooperative assistance in various ways, among which is the synod of bishops. The cardinals also assist him, as do other persons and various institutes according to the needs of the times. In his name and by his authority, all these persons and institutes fulfill the function entrusted to them for the good of all the churches, according to the norms defined by law.
Source: Code of Canon Law (Vatican.va)