"As a none steak eater I do know they are both beef but wouldn't have a clue at the difference between them so I m not far behind her"
Being an occasional steak eater doesn't help, Bluebelle. I don't know the difference either. Nor do I care much. If it's good meat I'll eat it; I'm not fussed about what it's called.
Actually, I might know a bit. Let's have a guess and then I'll go a-googling.
I reckon ribeye has something to do with the ribs so I guess meat under a rib.
Sirloin has something to do with the loin and 'sir' might be a corruption of 'sur' meaning above... so somewhere along the back.
<Googles meat cuts>
Well, whadyaknow, Mumsnet had the best answers. Apparently, "ribeye's tastier and juicier and sirloin has the the edge very very slightly on tenderness" (PogueMahone).
As regards where it is, I reckon my guesses are good enough. In short, I don't really care which bit of animal it's from so long as it's good meat, which both are.