can i choose any pikup that i want for a guitar? as long as it fits the hole? i am just starting to learn guitar so i really dont no anything bout guitars.

I don't know to much about pickup's (enough tho I'd love to learn)
but I know that it doesn't make a big difference...for a beginner. I know experts test things like that. So you don't have to worry till you develop your own signature sound and know what to buy.
For know, keep the one's in the guitar. If your getting one custom built, don't bother. It won't help much for someone starting out. Get a killer amp instead, or some effect's.

Pick-ups, strings, frets, neck size...all make a difference. But play around first, get good, then try swapping stuff out.

DUDE, single coil (the 3 in a line, last one slanted) work by picking up the vibtrations on those metal "dots". they are primitive at best nd usually come standard. save up 150.00 bucks and get at least the best single pickups you can find (won't be more than 150), but if ur guitar has humbucker (looks like two singles put together), they work together to pickup the sound more efficiently, than you can pick up really nice humbuckers for that price as well. BUT what you want is to upgrade to active pickups. they work by an electronic magnetic strip that can zone in on the vibrations however u the user wish them to. they can be as much as 250.00 a set but you can pick up good ones for 150.00 as well. the one that i got were the same price as the humbucker uprade would have been. 130.00 for the set.
i bet you want some brands?
the only brand i care about is EMG.
i'm sure others exist, somewhere.....

http://www.americanmusical.com/ItemSearch--search-active-pickups--srcin-1
i like sam ash, too, b/c these are the only not owned by musicians friend.
GC, MF, Music123, Sweetwater, same CEOs..........
And even though you'll practice a while before it would make a huge difference like everybody says, you should know bout what to expect and using good equip will help you sound good, beginner or expert. by knowing, u will also know where to put ur money when u do obtain some.......

Pick-ups make a huge difference.

With that being said, I agree with the guy above me.. don't start experimenting, enjoy the ones in the guitar.

Yes it does matter but while you're learning, if you are limited by price, then ask the person in music shop for best of worst. Also depends on what sort of amp or pa you pluggin into