How to add an image from the video to the beginning of composition? (Just an image, not a clip) I have a composition which is a union of 2 composition, and I want to add a snapshot from the composition to the beginning of it - is there any shortcut for it? 

I tried searching for it Google but did not find relevant results.
In the menu (at the top or by right-clicking a layer) choose Layer>Time>Freeze Frame

Adobe have a user's guide, it's a good place to start. Read more here.