Choose the Insert Keys Tool to place new keys on an existing animation curve. See Add keys to a curve.
Mutes the selected keys. Keys that are muted do not contribute to the animation on their channels.
When keys are muted, the following occurs:
Mute curves have the same number of keys as the muted keys animation curves, and their keys are positioned the same as those on the muted keys animation curves.
Unmutes the selected keys. Keys that are not muted contribute to the animation on their channels. Unmuting keys disables their Mute curves (indicated by the red symbol next to the names of the muted keys curves in the Graph Editor Outliner) but does not remove them.
To remove Mute curves, see Mute channels.