Inserting Frames

How to insert frames:

Highlight on the area of the timeline layer that requires frames. e.g. frames 24-30.
Right click and select "Insert Frame".

How to add frames (shortcut) Using the keyboard press "F5".

Note: Another way to create the effect of adding more frames between keyframes is to drag the keyframe to the right on the timeline see [How to drag frames and keyframes along the timeline].