search "action" or "string height"....maybe even "setup" there's plenty of info and resources for you!
Do you mean toward or away from the body? Like NJL said, that's "action". Up/down, as in towards the headstock or towards the back of the bridge, is "intonation". This is so that the notes at all the frets are in tune. All the info you need can be found with a search.
can u explain to me what it does when u move it up and explain 2 me when u put it down? and what do u mean by action?
http://www.garywillis.com/pages/bass/bassmanual/setupmanual.html Give each section a good read. It explains things pretty well.