Switch to the multiple key frame view (see Working with multiple key frames).

Select the key frame after or before which you want to add a new key frame.

Choose Edit → Add Key Frame or Edit → Insert Key Frame.

You can also press Enter which is the same as Edit → Add Key Frame.

Select a motion path and open the key frame panel (see Working with the key frame panel).

Select the key frame after or before which to add a new key frame.

Choose Edit → Insert Key Frame to insert before the selected key frame.

You can also press the + button in the key frame in the key frame panel or choose Edit → Add Key Frame or press Enter.