Here you can find an overview of Rigging Tutorials. Rigs or Armatures are extremely useful for animating. When properly configured, it can serve as the skeleton of a human body or other kind of mesh and can make animating go a lot easier and quicker. Not only can it move (parts of) a mesh, it can also deform it.
But setting up a rig can be confusing. Especially with big armatures and things like inverse kinematics. Start learning everything about it right here!