To take screenshots, you have to press CTRL+PRNTSCRN. You can then find the screenshots under My Docs\My Games\GC2TwilightArnor\ScreenShots.
Just as an FYI, this site doesn't allow you to upload pictures (or any other files) directly. You have to upload them to a hosting site (like Dropbox) first, and then link to them in your post (use the icon with the tree-symbol on it for this).