Magnanakaw, Mag-aaral

Hello for "magnanakaw" and "mag-aaral" these could respectively be translated to "thief" and "student" right?

I was just wondering why that would be because isn't "mag" for verbs? or is this just another option or technique for those words. and would this be allowed for other words like "magtitinda" or "mag piprint" like "seller" and "printer person"