I push the buttons and things happen. Did you try that? I use imgur.com to process my images. Someone else might have an awesome explanation but my not so awesome one goes like this. I go to imgur.com and hit new post. Then browse to find the image you are looking for in your screenshot folder. Once it uploads to imgur, you mouse over the image and open the "get share links" option. From there, copy the BBCode link and then paste it into the BBCode tab at the bottom of your forum post. If you are replying to a post, you have to hit the "reply" button to see the BBCode tab. And, if that makes no sense, then hopefully someone who is smarter than me can share a better explanation!