Just bought first Apple, a MacBook Pro, so new to apps and sorry for prob very basic question. Have been playing with iMovie. Want to take a frame from video footage and export as a photo/jpeg/still image. Have tried using help, but must be typing in the wrong search terms. Im sure Im not the only one who has wanted to do this (but maybe the only one who couldn't figure out how!) Could you please tell me (in terms a beginner can understand) how I can do this?