Hit the PrintScreen key. The screenshot will be saved in .TGA format in your 'Il2 Sturmovik' folder as 'grab0000.tga','grab0001.tga' etc. You'll need an imaging tool (Photoshop, MSPaint) to convert it into .jpg format(if you don't have such a tool yet - IrfanView is a free download http://www.irfanview.com).
Be sure to move your favorite screenshots out of the folder, as they will be written over the next time you load the game and save a screen shot.
Be sure to move your favorite screenshots out of the folder, as they will be written over the next time you load the game and save a screen shot.