There are four main branches of oceanography: geological oceanography, chemical oceanography, physical oceanography, and marine oceanography.
Geological oceanography is the study of the shape and geological features of the ocean floor, like underwater mountains, trenches, and even... sometimes... VOLCANOES.
Chemical oceanography is the study of what chemicals are in the ocean.
Physical oceanography is the study of the temperature, density, and pressure of seawater. It also discusses the forces that cause tides.
Marine oceanography is about the plants and animals that live inside the world's oceans.