First, do a search in these forums for "still"; there has been a lot of
discussion on this matter already.

To save a still image of a frame, cue the timeline to the frame and then
click on the floppy disk icon at the top of the preview window. What gets
saved is basically a print-screen version of the frame, so you may want
to resize the preview window first.

As to your second question, i'm not sure if you're asking about the
single frame you want to save as a still image or if you're asking about
cutting out parts of the video picture in general. If it's the still image,
then just open up the still you've saved in any photo editing software
and crop it. If you want to crop the video in your project, check out the
pan & crop tools in Video Factory.