After you get the 'Lawbringer' perk, you visit the Regulators HQ and find a terminal on one of the rooms, along with a computer system.
Accessing the terminal, you find that you can accept contracts on fugitives who are wanted by the law. You are to give them some 'Wasteland Justice'!
The missions start out easy and get more difficult as you go along. You will be traveling to various locations, each with their own map marker. Many of the places are new, some include interiors, and all have a lot of combat waiting for you. Find the 'Boss' and take him out and bring the fugatives finger back for your reward. Your enemies include Ghoul Raiders, Raiders, Slavers, Talon Company Mercs, and even an assult on an Enclave base and Super Mutant base.
If you complete all of these missions without canceling any of them, you will be rewarded with a perk that gives 10% Damage Resistance, 10% to your Critical Hit chance and 20% Chameleon when you are sneaking.
For each contract you collect on, you will get caps and a karma increase. Your stats can also be displayed on the computer on how your doing.
You can also purchase upgrades for the Regulator compound, including 4 Heavy Gun equipped Regulators (1 patrols the yard, the other 3 are in towers) and up to 14 turrets you can purchase around the base.