Hi, Tiffany,
It is a bit early for you to start yet, but in a couple of years you should be looking to help at a horse livery stable or riding school, a boarding kennels or cattery, on a farm, or anywhere where animals are kept.
Later on, when you are 15 or 16 ask a vet if you may spend a few days in the practice.
Unfortunatly it has become more difficult for someone like you to find these opportunities because of the stupidities of current 'Health and Welfare' legislation, since the owners of these places are terrified of there being an accident with an animal and their being prosecuted and sued!
W