To make the screenshot, just press the Print Screen key, open Irfanview and select Edit/Paste.
Then position your cursor on the top-left corner of the bit you want to show, hold the left mouse button down, and pull down and right. You'll see a rectangle on the screen. Let go of the mouse button when you have the proper cut-out. Start again if you don't get it right straight away. When satisfied, in Irfanview click on Edit/Crop selection.
Then click on File/Safe as xxx.jpg and attach that to your post.