when you rep somebody (clicking on the star in a post) he/she gets reputation points for a good map/tutorial/or what ever you find rep-worthy ... could even be really good advice. You get the option of writing a small note too if you want. The little green pip under your guild title (over your picture) shows how much rep you got (a pip pr started 100) - you give out 1+pips+something else like how long you've been member and stuff ... you can only rep (with points) when you reach 10, but rep without points added is nice too - cause when people rep you, the acknowledge you've done something good or nice
So swing that twig of repping +1 you got if you see something worth it