What Federal Jobs can I get with just a highschool diploma?

I’am currently working as a lifeguard for the city of long beach, its a great jobs, but its time to do something more serious. I’am planning to apply for a local police department once I reach the age of 21. Until then I would like to work for the government so I gain experience. Are there any jobs within the government which only require a high school diploma, and if they do. Where do i go, where and how do I apply, and should I make a whole bunch of copies of my resume?