How do I become a police officer

Go to the Police Academy.

Get a degree in Criminal Justice or some related course.

Join the armed forces and get trained to be a Military Policeman.

In Florida some community colleges off classes so you can get your Law Enforcement Certificate.

For some, you finish high school. Apply. They will send you to a police academy.
It will help if you go to university and get a 4 year degree. It can be in Criminal Justice, but it can really be in anything.

Also people who have served in the military are often given first chance at employment.

In some areas, you pay for yourself to go to the police academy and at graduation local departments may offer positions.

It depends on where you live. Here in CA, you apply for a job, interview, test, etc. If you pass the testing and background checks, they send you to an academy where you are trained. You receive more on the job training after that, or work in the prisons while you await an opening at a station.