The compulsory levels have been explained well already so I'll just comment on the optionals.
So, optionals (8-10) have a scoring system made of 2 parts; execution, and difficulty. The execution, or 'E' score, starts at 10.0, and deductions are taken from that. This is where all the usual form deductions, falls, etc are taken.
Then we have difficulty or 'D' score, which is where things get complicated. I doubt you'll want to hear an in depth review of how it works so I'll try and keep it brief! Basically, every skill has a point value. You add up the values for the top ten skills (8 skills for level 8's and 9's) and that's part of your D score. The other part of the D score is the requirements. Every routine on every event has to fulfill certain requirements, for example on floor you have to flip forwards, backwards, do a press, etc. for every requirement you fulfill, .5 is added to your D score. Level 8's have 3 requirements and 9/10 have 5. So, you add up the value of your top skills, then add that to the value you get from fulfilling the requirements and that becomes your D score. This score stays constant (well, most of the time, but we won't get into that!)
So, you add the D score to the E score, and you get your start value, or max score for that particular routine. Deductions are taken (From the E score) to come up with a final score. So long story short, the maximum score will be different for every routine. Most level 10's will be scoring 13's and 14's. College and elites will be scoring 14's, 15's, and sometimes 16's.