lenses... please explain...

hi, im looking at purcgasing a secondary lens for my SLT-A55. currently i am using a 18-55 and just want a little bit more info on what other lenses are available and there uses. I here alot of talk about the various types of lenses available but just cant seem to put it all together. Could someone please give me a basic explanation as to what lenses are best suited for different types of photography... Or a link?

Thanks guys.