All righty then...
You might check out
this link... It's something I wrote sometime back about the application process.
Now...
You want to become a cop because you don't like how the military is treating soldiers. You really think cops, feds, or other LEOs get treated better?
Law enforcement is more than merely profession or career. It's a demanding calling; being a cop WILL change how you view yourself, your family, everyone you deal with... It's tremendously demanding, and tremendously stressful. It's also incredibly rewarding -- even if the financial rewards suck, and the brass drives you nuts. Others have mentioned Explorers; you can find Explorers or similar programs sponsored by many police departments. The program is similar to JROTC; it's career education and community service. There are also law enforcement programs in some high schools, that give students good exposure to what police work is really like.
As to feds... If you go fed, you pretty much WILL be expected to move as the agency demands. For some federal agencies, if you don't do sufficient time in various places, including a headquarters tour, you won't move up the ladder. To me, what most feds do is boring. It's mostly paper chases and paper work. Feds DO, with very few exceptions, require a 4-year degree. Most state police departments also will expect you to be willing to move to where they need you within the state.
Education-wise -- most police departments don't require college. Some require it for advancement, and the days of a police chief without at least a bachelor's (and often a master's or higher) are slipping by. Even in a 6 or 7 man department, there's just so much that the chief has to know beyond being a good cop... Some, but not all, forces will pay you more for a degree. That said -- few US agencies hire people as cops below age 21. You've got 3 basic choices about what to do with that time, because sitting on your *** and doing nothing is a non-starter. You can work, in some capacity, and get some decent life history and show responsibility. You'll find that almost any job has some usefulness in law enforcement... Or you can join the military. Cost/benefits there are covered well by others -- but there IS a war on, and you've got other concerns there. Finally, you can go to school... The bottom line here is simple: You can't spend 3 or 4 years going to parties, spinning your wheels, and doing nothing even in the current climate where agencies are fighting hard for a small talent pool.
Your background will be examined. That assault will come up; be ready to explain it. It's most likely that, with a decent and honest explanation, it won't be a problem. What they will want to know is that your judgement has improved; in today's world, the liability of hiring a cop who can't rein in their temper is not something that anyone can tolerate. Stay away from drugs, alcohol, and do your best to avoid "stupid kid stunts." You also need a good driving record.
Languages... Learn at least one. Start now. And learn it right, not what some of your buddies feel like teaching you. (For example... at least in my area, calling Latinos "Chicanos" would not go over especially well...) I don't know what happened between you and the Spanish teacher at your school; in all honesty, given some of your posts, I've got a feeling that the communication problem that led to you being insulted was probably 2-way. Spanish is very useful and may be required soon in at least some areas. Asian languages are also highly desired in many places. Middle Eastern languages are of special interest federally, for obvious reasons.
I'd also suggest looking at several of the police related forums on the internet. Be cautious; there are lots of posers and wannabes on the web who aren't half of what they claim to be. I personally suggest
Law Enforcement Forums simply because they make it clear who is and is not a real cop -- and they have a very stringent verification process. But, you've got to understand that particular site is run by cops, for cops, and it's got a certain feel because of that.
Right now -- this is what I'd suggest you do. Keep researching career options. If you don't go into the military, I encourage you to go to school. And to work. Getting out on your own after high school isn't a bad thing. But the main thing is to keep researching lots of careers. I bet your interests change at least once more before you graduate.