In all of Canada we use the FIG scoring system, therefore your routine is based on two parts.
The A, or exectuion, score is out of 10, this is where they take off all the deductions for mistakes you make.
The ohter part is the B, score, which is for the scores you perform. At each level there are EGR's, required skills, that you must perform and are usually worth 0.5 each. Then there are your bonus skills that you can perform for extra points.
One judge calculates your B score, the other your A score and then they are added together to give your total.
In the USAG and NCAA they use the 10, but after compulsories not all routines start at a 10. The highest start value is a 10, but if a gymmie does not have all the required elements the start value can be lower.
The deductions are different too, a fall is 0.5, whereas in Canada it is 0.8, next year the fall will be 1.0.
Most of the world now uses the FIG system, including the MAG system in the US.
Hope this helps. Here is a link to the basic charts for P1-P5, this will give you an idea of the skills required and the bonus available on each apparatus.