From now on, when someone posts there will be a small + in the post. Click that to give someone reputation.
Furthermore, each person may only give out 2 reputation every day.
If you want to + someone twice, you will have to wait 30 seconds between each.
Reputation is a small sign of thanks from player to player. If somebody gets 100 rep, they can buy Modship from the PokeDollar shop (aslong as they have 30,000 PokeDollars).
Basically, if you have alot of reputation, people respect you. This is why 100 reputation points is a good reason to be a mod.