In other words, I don't know when, it just shows up on the schedule whenever it is ready to show up. I don't even know where it will air this time- it could be Cartoon Network again, yet it could also be Boomerang or the Cartoon Network website. All I can say is wait and see.
When you've paused the DVD on the scene you want, that's when you take a screenshot, or screengrab, from the DVD program (make sure it's in fullscreen so that it's the only thing on the screen, and that it's clear of any menus). Then paste it on a Paint application (or whatever program you have for pictures). Edit it as needed (i.e. crop out black bars), save it, and it'll be ready to upload on here.
Just any photo editor application should do. For Microsoft, there's Paint (which I've used) and Windows Photo Gallery. If you don't have Microsoft, there should be an equivalent of some sort for whatever you do have.