How does it work? I need to know for everyday use and BF2.

Alright.
When you press Print Screen, it basically puts a picture of your screen onto your clipboard. Later, you can go into Paint and paste it, then save it.
I like programs like the UO Screenshot Utility or Fraps better though since they automatically save to files.

EDIT: Fixed links, and no problem.

Thank You

Correction: The PrintScreen button is the official SWBF2 screenshot button! It saves the screenshots in the \Star Wars Battlefront II\GameData\ScreenShots\-directory!

If it doesn't (depends on your system) work try this:
1. Create a folder called "ScreenShots" in the following directory: \Star Wars Battlefront II\GameData\
2. Hold the ingame screenshot button for about 1-2 seconds when you want to take a screenshot!

Hope this helps!

GrabClipSave is equally an efficient screen-capture utility...