When you see something you like, get great advice, or otherwise want to express your gratitude, you can give points. If you click on the scale icon at the top of someone's post, it says add to reputation (you are giving "reputation" points). It allows you to write a short note, and gives the person a point. Enough points equals a green reputation tile, and thus you can see how reputable the person posting is...YMMV, batteries not included.