Ceratopsians, meaning "horned faces" were a group of dinosaurs that, hence the name, had horns on their faces.
Protoceratops, one of the earliest Ceratopsians has not evolved horns yet, but had a very hard head. Later Ceratopsians evolve all kinds of different horns: some Ceratopsians had one large horn going strait up on the front of their head, such as Centrosaurus. Another good example is the Styracosaurus, who also has a very spiky crest. Einiosaurus doesn't have a strait up horn, but rather, a horn that spikes outward, good for bashing predators. Then some Ceratopsians, such as Triceratops and Chasmosaurus have a single small horn on the front of their face, and two larger horns up by their eyes. Then finally Pachyrhinosaurus has a larger horn on it's nose, and a smaller horn behind it, simillar to a Rhinoceras