That will tell you how to take a screenshot and where the screenshot will be located. It also gives you a link to a site where you can upload your screenshots for free - just remember to convert the screenshots to .jpg format first to shrink their size. You can use Windows Paint to do that if you don't want to (or aren't allowed to) download and install a 3rd party picture editing program.
Then when you make a post just use the URL link that the image host site gives you to link to the screenshot.