screwed up with programs: mostly itunes


i'm pretty new to mac, and since i couldnt find the uninstall packet, i just deleted it...thats the right thing isnt it? and so i did. but now i need itunes back and when i download the package for mac os x and tried to install it, i cant check the box for installation to install it. so i was wondering how can i get itunes back? and how do i uninstall programs the right way?