Osnail

Ok so before you all start shouting 'Noob' and throwing rotten veg, I'm still learning and failing a lot... I'm struggling with some downloads I made - When I open MFME X.x it tells me that I need to open in a different one, then it just says ROM missing, wrong password... etc etc Am I opening in the wrong version or are the downloads the issue. When others seem to be using them all ok, I'm sure the issue is me. Is there a sure fire way to know which EMU to use?