Open the pm, press "Print screen" key on your keyboard. Then go to microsoft paint or any other graphical software and press "ctrl + v". The printed screen will be pasted as an image. You can then save it (file -> save) and upload it to www.imgur.com.
Just download gyazo from http://gyazo.com/, install it, run it and draw a rectangle over the part of the screen you want to have in your screenshot. A new browser tab will open with your screenshot ready.