I see speakers on many monitors but what are they for? My montor has 2 speakers but I've never heard any noise from them. I am not a fan of speakers and I would be happy if I can remove my bulkey speakers and use the monitor's instead.
They are what any speakers are used for, sound. There should be a 3.5mm jack connected to them in some way.
If you have separate speakers, you're better of staying with them. They'll produce much better sound than any built in monitor speaker.
Monitor speakers are usually only a couple of watts max, they're fine for system sounds / alerts but music you're better off going with a separate system.