During character creation you have 6 mutant points. Each power's cost equals the level of the power. So a class 1 power is 1 point and a class 5 power is 5 points.

The powers you have all start at level 1. You can increase the level of your powers by spending mutant points. The cost to level up a power is equal to the class level of the power.

As you level up you get 1 mutant point which you can use to increase you mutant powers level or obtain a new power.