This quick tutorial will show how to animate a rig. Before following these steps, first create a mesh and apply a bone rigging to it. Once this is complete and done correctly, you can begin animating.
The first step is to switch into Pose Mode. In this mode you can select bones, pose them, and keyframe [i] as usual. For the very first frame, keyframe as LocRot. Also make sure to select-all-bones every time you key frame.
For all other keyframes, use Available.
Note: If you mess up, you can always move back to a previous keyframe and use Available to override it.