From BlenderWiki

Animation Editors

Animation is a big task, often involving repetitive work. This is why many different techniques have been developed over the years, to hasten, and reduce the workload facing animators.

To manage all these features, Blender has several Animation editor windows:

The Timeline

The timeline does not allow editing of animation data, but displays all keyframes of a scene. You can edit Animation Markers in the timeline.

The Graph Editor

This is the lowest-level editor, where you use one curve to control each animated property/setting/channel.

The Dope Sheet

The Dope Sheet (Previously the Action Editor) has Four modes of use. Each are very similar, but work with different types of animation data:

Dope Sheet Mode

This is a general keyframe editor, which displays all keyed channels of all scene objects.

Action Editor Mode

This is similar to the Dope Sheet mode, but displays per-object keyframes, and is specific for creating Actions.

Shape Key Editor Mode

This displays shape key animations for selected objects.

Grease Pencil Mode

This displays grease pencil animation data that you have done.

The NLA editor

The idea behind this high-level editor is borrowed from the non-linear video editors: each element represents an action, which you can move, duplicate, shrink/pull (i.e. fasten/slow down), etc., to your liking. If keys are like mesh faces, an 'NLA action' is an object encapsulating those mesh faces, with a modifier.

The important thing to understand is how the progression of animation data is reflected by the animation editors:

• Keyframes form animation Curves,
• ...Which are used to create Actions
• ...Which are used by the NLA.