just click the scale on the bottom beside the report button and beside the online/offline button and select i approve and click add to rep.
on the left side of the post, where it has your name and junk, there is a little icon at the bottom that looks like a weight, it's white, press that and you can either give them + or - rep.
but if you give them -rep then you have to give a reason, and it has to be a good one or youll get infracted.
wow, forum rules these days. But, to stay on topic, listen to the guy above, cause you can't just go around - repping people for the fun of it.