If I need a capture of a screenshot of something cool in my game, I hit "Prt Sc" on the keyboard and then I'll "Paste" it into a new composition in Photoshop and crop/resize it. Then I save it as a jpeg to upload.
If I'm on the PC, that's what I do sometimes, too.
Sometimes all I have to do is "print screen," though, and some games will automatically save it. For example, World of Warcraft and Steam games have a built-in system to take care of it.
LOL I do that when i'm gaming on the PC. However if i gotta capture my console games I haven't found a solid way of doing that yet. I been thinking of getting a capture card but not sure yet.