People give you reputation. They give it to you when you make a deal or a deal goes smooth between you and the seller/buyer. Reputation doesn't do much, considering it's given out commonly but it's normally a sign in trust. If you have anymore questions, shoot me a PM and welcome to the fourum
You can simply earn Reputation by being around the forum, hosting contests, giveaways and much more. What reputation does it tells if you are HQ, or not.
Positive (Green) reputation = Good
Negative (Red) reputation = Bad