Are you talking about in your car or in general? In the car the only AC Circuit should be the Alternator AFAIK
If you are testing an outlet from a wall or something, that would be AC - if you are testing an electronic device (after its PSU and such) you are almost certainly looking at DC unless its a unique application
As for will you damage the meter, good question. Maybe someone more experienced can chime in, i'd say it depends on the quality. I have used cheapo ones that exploded for nearly no reason at all, and good ones that I guess have mini circuit breakers built in or something.