Animate objects or skeletons by setting markers (keys) to indicate timing and position.
Keyframe animation lets you transform objects or skeletons over time by setting keyframes. For example, you can keyframe the joints and IK handles of a character’s arm to create an animation of its arm waving. You can set keyframes (also known as keys) by selecting an object and selecting from the Key menu in the Animation menu set or pressing S on the keyboard.
Keys are arbitrary markers that specify the property values of an object at a particular time. Setting keys is the process of creating the markers that specify timing and action in your animation. Animation is the process of creating and editing the properties of objects that change over time.
For a short video that explains the basics of keyframing animation, see the Keyframe Animation in the 1-Minute Startup Movies. For a tutorial that explains the basics of keyframe animation, see Animating an assembly line - Part 1: Keyframe animation.
Once you create an object you want to animate, you set keys that represent when the attributes of that object change during your animation. Setting a key involves moving to the time where you want to establish a value for an attribute, setting that value, then placing a key there. In effect, you are recording a snapshot of the attribute at that time.
You can rearrange, remove, and duplicate keys and sequences of keys. For example, you can copy the animated properties of one object onto another, or you can stretch a chunk of animation over a longer period of time than you originally keyed.
See Set Keys and Edit Keys for information on how to create keyed animation.