I think, especially when you're young, you learn where and when you are called by trying out different things and finding what fits you and where you see God move. Done more short term trips than I can count and a good one is not exactly like anything else you'll ever do or attempt. Expect super budget accomodations (like summer camp or other camping or youth hostel), strange but tasty food, to be partially confused most of the time, and to find yourself in situations where you have to figure out a way to do something because you're there and it needs doing. And expect to feel a special connection with the people you're serving once it's over.
Lots of organizations have open teams where anyone from around the country can apply to go on a trip with other people from around the country. Figure out how you'd like to serve and for about how long and take to google to see what opportunities are available (seriously a search about short term missions trips or mission internships should give you plenty of results).