The PRS Parameters rollout provides tools for creating and deleting keys. PRS stands for the three basic transform controllers: Position, Rotation, and Scale.
To create a PRS transform key:
If a particular Position, Rotation, or Scale controller doesn't use keys, then that button is not available under Create Key. For example, you can’t create Position keys if you're using a Noise Position controller.
Creates or deletes a move, rotate, or scale key at the current frame. These buttons become active or inactive depending on the existence of a key type at the current frame.
For example, if you're on a frame containing a Scale key, the Scale button is inactive in the Create column because a key already exists. At the same time, the Position and Rotation buttons are inactive in the Delete column because there are no keys of that type to delete.