To get any kind of job in this world you usually need to have certain qualifications and requirements that must be filled in order to get that job. I believe the job with the most requirements and expectations that have to be met is in the field of law enforcement. There are basic requirements like age. Then there are more complicated ones like education. Overall I believe that law enforcement is one of the hardest careers to get into.
From a very young age you must begin doing certain things in order to get into law enforcement later on in life. One of these things is called many names in different departments but the purpose remains the same and that is volunteer work. Basically you run security at fairs or games and run traffic at big events. When you hit the age of 18 you can apply for what is called the sheriff's patrol. This is a more hands on experience with law enforcement where you actually get to respond to calls and do most of the things a full time officer does. You do all this without getting paid because it gives you a lot of credit with a department when you become of age to apply for a full time position.
When you hit the age the department you are applying for requires you must meet many more new requirements. The first requirement is to take a test called a P.O.S.T test or police officer standards test. It is a general knowledge test not unlike the SAT's or ACT's. Usually on the same day you must take a physical agility test. The reason you have to do these tests is to weed out the "dead wood" from which the department will take the top ten applicants. If you make it into the top ten list the senior people at that department interview you. The department will then take the best applicants out of those ten for however many positions they are looking to fill. This is all done to get the best of the best to fill the spots they need to fill.
If you are lucky enough to be one of the applicants chosen to fill a position you still have a long road ahead of you before you are a full time officer.