Talk with referees at a game, contact the athletic department of a local high school or contact your local recreation department. They will be able to give you the name of the state governing body for high school athletics. You will be expected to complete a registration form for affiliation with a national, statewide or local association. Often there will be a fee that must be paid with this registration which goes toward additional officiating training and insurance. Often, with your state association fee, you will be provided rulebooks and other materials.
Many programs offer no pay.
Game fees in other leagues vary widely based on the players' age group, competitive level and the state you officiate in. Ask a respected veteran referee to be your mentor if one is not assigned to you. That mentor will help answer your questions and provide crucial support. Don't be afraid to ask questions about situations and rules. The more you talk about officiating, the more you will learn about it.