You put a heading titled: "Experience." Then you list three for four places you have experience doing this and under each place you tell the skills you used.

Or you could do a heading called: "Skills" and list the skills you have developed. You might make a cover letter to go with your resume where you could elaborate on your skills and where you learned/used them. I think applications also have a spot where they ask you to list other skills you have developed. There you could list your skills and where you learned/used them. This is where you would elaborate on your volunteer experiences.

Good luck on getting a job.