My dog has fleas; how to get rid of them and how fast do they spread?

so my dog has fleas and we noticed ONE last week and ONE more a few days ago and i saw 2 today. but now i dont see any more. she is a white dog. so its been a week so how much do you think they spreaded?????? and they look like black little bugs with 2 antennaes and a few legs so is that flea's??? and we put flea powder on her but i still saw 2 today.... HOW FAST DO THEY SPREAD AND HOW DO I GET RID OF THEM(if they are flea's..) please help! thanks :)