To copy recorded video, select all or part of the video (see Selecting Video) and choose Edit->Copy (Cmd-C).

To paste video into an empty Videator window, select the window and choose Paste (Cmd-V).

To paste video at the end of a recorded video, go to the window with the recorded video and choose Add to Movie (Shift-Cmd-V) from the Edit menu. 

To paste video into a recorded video:

1. Move the Out marker to where you want the video to be inserted.
2. Choose Paste (Cmd-V) or Add to Selection (Control-Cmd-V) from the Edit menu.