You can add frames using:
- Frame > New Frame (
Alt+N): Creates a copy of the current frame in the next position.
- Frame > New Empty Frame (
Alt+B): Creates a new empty frame. (All transparent layers with an empty cel, and the Background layer is cleared with the active background color.)
- Frame > Duplicated Cels (
Alt+D): Copies the current cel, or creates a copy of the current Timeline selection, into the next position/frame.
- Frame > Duplicated Linked Cels (
Alt+M): Creates links to the current cel (or the current Timeline selection) into the next position/frame.
+ in the status bar can be used to add new frames (it's like pressing