The levels are to express your rank basically, they give you special rights inthe long run, you can get experience through posting in topics and being active, and for testing people, in the long run testing will rack yu up a ton of experience.
Level 1: 1 EXP
Level 2: 100 EXP
Level 3: 250 EXP
Level 4: 500 EXP
Level 5: 750 EXP
Level 6: 1150 EXP
Level 7: 1400 EXP
Level 8: 1800 EXP
Level 9: 2000 EXP
Level 10: 2500 EXP
Level 11: 3000 EXP
Level 12: 4000 EXP
Level 13: 6000 EXP
Level 14: 8000 EXP
Level 15: 10000 EXP