The skills you can gain by volunteering can be all sorts of things. You'll learn to work better with groups of people, and valuable leadership skills are gained as you help and talk to new members. You might get to work with computers and help address letters which are data entry skills.
Best of all volunteering is itself something to put on job and college applications. You'll get to do something that you (hopefully) enjoy, and it can help you land your dream school or a better paying job!
Yes you can learn many skills from volunteering, especially if you are volunteering in the profession you are interested in. For example if you want to work as a vet tech or veterinarian volunteering in a vet office will show you the day to day happenings in the clinic. You will then pick up the skills needed to do that job. Also by being there you could determine if that is really something you want to do.