To make a screen shot you can use your computer. Just head over to hulu.com and find the episode you want to take a screen shot from. If its a recent one than your in luck since all the recent episodes are available to re watch.
When your watching the episode it pretty much works like a youtube video, so easy to find the shot you want to make. it might be a good idea to hit the full screen button to get a good shot
Than hit the print screen button on your keyboard. Typically located around the same place as the home, scroll lock, and insert key. Now open up MS Paint, commonly called Paint, (if your using windows, idk what mac users do for this part) and hit the edit menu on the top, and hit paste. If you want to mess with the other stuff you can do with Paint go ahead.
Now save that picture. Now head to photobucket.com, you might need to make an account. This is pretty much a place to easily upload photos. Its a great site for things like thing. After you have your account there should be an upload button somewhere. Go ahead and hit it, find your picture and upload it. Now somewhere around the picture it will say share, click this than you want to copy the URL, thats all you need.
Than come here and paste the URL into a new forum post and than high light it and hit img button.
Hopefully this helped.