This question is regularly asked, as a search would quickly find. Here is an answer provided by John:

"Move the timeline cursor to the point in the video where you want to take a still image from - select an area where there is little movement for best quality.

Then select File, Export movie, Single frame as jpg - set up where you want to file saved and and any other options you need then click OK.

There is an installed pdf manual available in the program under Help, pdf Manual - it is worth reading this."

I don't do stereo -- you may have to temporarily change your preoject settings if the editing preview shows side-by-side.

Regards,

Carl