I don't understand

hey everybody
I desperately need some help. I'm a 14 year old girl who's working with a mac for the very first time. I really want limewire at my computer but when I downloaded it, limewire opens as a document and it tells there's no program available to open the document. Help me!!! how do I get limewire on my computer?? When I say: choose program I can only choose programs like I-Tunes and there's no limewire there.
sera