Highs and tweeters

Whats good man, liek i said before im not too car savy, i dont know much about alot shit when it coems to cars which is kinda embarassing. But anyway, I just got a car stereo for my 98 crown vic, and i wanted to start fixing her up, so i was thinking about starting with the inside. I need help though, what, specificly, are highs? I know they are smaller speakers, like the 6x9's, but if i do get the 6x9's and tweeters, will the scream like highs are supposed to? and also do i need an amp for my highs, i need ya'll help man, lol im supposed to go get these on the 1st man, cant go make an ass out myself so ya'll help will be greatly appreciated, thanks