When you make a user, you'll have 10 points.
You will get:
2 bars at 100
3 bars at 200
4 bars at 300
5 bars at 400
6 bars at 600 (light green)
7 bars at 800 (light green)
8 bars at 1000 (light green)
You can check your amount of points in the User CP
Users with red rep gives nothing, you wont increase if they rep you and you wont decrease if they derep you.
The more posts and rep you got, the more rep points you give.