In APB you have two faction you can choose from: Criminals, and Enforcements.
Here we are gonna talk 'bout the Enforcements.

What are the enforcements?
Enforcements are cops. Their mission is to catch the criminals.
How do i earn point?
You'll earn points by arrest the criminals, with those points you can buy weapons and clothes.
How will i know where the Criminals are?
When a criminal commits a crime, the cops get an message and a icon on their mini-map.
Every criminal has points/ranks, and you as cop get only the criminals that have the same rank/points as you. So your skills will be most likely equal to each other.
Can i buy a car/clothes?
We dont know if you can buy better police cars, but atleast we know you can buy new clothes the more points you get, so you can make an Urban style policeman or just a standard cop, It's your decision.

More info later...