How to make screen sot from render?

To save the render hit F3 and save the file making sure to put it’s suffix, (i.e. .tga or .jpg, whatever format you have it set to in your render buttons window).

To make a screenshot, (and this is Windows), hit Print Screen button, go to the Paint program, go to Edit and hit Paste. Then save as whatever. If you have Gimp, (and you should), go to Aquire and From Screenshot and use that function and you can screenshot just the window you want. Most photo editing programs have a similar function too.

as well as F3 to save your render:

ctrl-F3 saves the 3d view
shift-ctrl-F3 save the entire Blender window