Depends on the game, sometimes it is the spacebar, or maybe just a mouseclick...
A quick and dirty screenshot is the printscreen key, then open a graphics program, or Word processor, and depress control - V (another way to paste)
<pre><font color=red>°¤o,¸¸¸,o¤°`°¤o \\// o¤°`°¤o,¸¸¸,o¤°
And the sign says "You got to have a membership card to get inside" Huh
So I got me a pen and paper And I made up my own little sign</pre><p></font color=red>