well first you accomplish something. Then, if on a mac, you use shift + cmd + 4 to take a screenshot of the area you want, which would then be a square that you extend with the tool. Then you upload it somewhere, for example tinypic.com or imgur.com.
THEN you right click on the picture and click "Copy Linkadress" or something like that (I have my browser set to danish so i really have no fucking idea :])
THEN you go to where you want to brag about your achievements, click the Image input button or type