I have a "95" buick park ave and I replaced the starter, I think i might have done

[???]

something wrong...? The original had only two post the new one had three.... so being a girl and considering one was marked s and one r I went with s for starter.All it does is click when I turn the key,and when I went back to the parts store and asked the guys they started argueing about it. I'm confused and cant afford a mechanic...really any help would be great...Thanks