As a High School student with no previous job experience I would suggest that you start applying to paid part-time jobs...in other words jobs where you are working for a few hours a week or during the weekends, such as cashier at a local grocery chain...
In this way you can begin to understand different job roles and how a business operates and your role in contributing by working with others and under the direction of a manager. This will help you begin to build a skills resume that you will need to be able to move to other jobs that may interest you. You will also be able to pick up referrals from your manager(s) that are invaluable for future career movement. You won't know if you like the water until you get in the pool !
Ken offered some great tips for locating opportunities but I have found that if you "talk it up" at school someone invariably knows who may be hiring and can give you a lead. But don't hesitate to go and fill out applications to give yourself as many opportunities as possible!