The concept of saints is common throughout Christianity. The Apostle's Creed (affirmed by all mainstream Christian denominations) states belief in the "communion of saints." But there are significant differences in beliefs and rituals among Christian denominations when it comes to the saints.
Saints in Catholic and Orthodox Christianity
Saints play a prominent role in the rituals of Roman Catholic and Eastern Orthodox Christianity. Both branches canonize saints, recognize saints' feast days, name churches after saints, display icons and statues of saints, and pray to saints to intercede for them before God.
This set of practices is sometimes called the "cult of the saints" (not in the sense of a sect, but in the sense of the Latin word cultus, worship). In both Catholicism and Orthodoxy, the Virgin Mary is the preeminent saint.
Saints in Protestant Christianity
For most Protestants, great Christians of history are people to be admired and emulated, but not called upon in prayer. Protestants generally make little to no mention of the saints in worship and have no rituals related to the saints.
Some Christian denominations, such as Lutherans and Episcopalians, name churches after saints and recognize some saints' days, but they do not canonize saints or emphasize the intercession of saints.