Hi Ethel. Does your school have a multi-media program? If so, you can start by reporting on your school's local games. You can write for your school newspaper. You could announce the games, meets and matches on-site at your school.
Outside your school you can try to get an internship at a local TV station or radio station. Do any of the local networks cover high school sports? MSG network has a high school sports network in NY and my son submitted some video of himself broadcasting for his high school sports channel and won and award, got to a live report on one of their shows and received scholarship money. He later got a summer internship with Fox and I am pretty sure it was that experience with MSG that got him the internship.
Be creative and use your high school sports programs as an opportunity to develop your writing and on camera reporting skills. Then look to your community for local stations and reach out for internships. Good luck!