When you rep someone you are letting them know that you appreciate their post, We played a game with it for years to see who could get the most points. Kinda blew it's value some but it was fun. I never could lead the race though, They always neg repped me. A newbie maight can only give you one point with a rep and one that is maxxed out can give you more than a million.
To rep someone look in the persons post and down on the bottom left you will see a star. Click on it and a box will pop up and you can give them positive if you like what they posted or negative if you don't.A lot of us on this thread are maxxed out. The more points you have the more points you can give someone.
Likes are another way of showing you like their post and whole lot easier as with rep you have to rep 75 members before you can rep them again. But you can only like a post one time. Just click on the word like in the bottom left of thei post.
Credits are a point system that was installed a couple years ago, You get so many points for posting and starting a new thread also i point for repping each time. If you look at the top you will see Market. You can go there and spend your credits. You can change the color of your username or even change it there. There are a number of things you can do. Hope all this helps.
Rep'd, and Liked because with a little knowledge, I wanted to go wild. Thanks for the explanation.