You start with "open slots". Open slots can be used once per reset, then are reverted to blank next reset.
You may permanently assign a slot to be a certain power, then it uses that power forever at the cost you gave.
Note that powers may not work exactly the same way each time you use them.
The power cost is variable, but generally Minor is 1-10, Major is 2-50, Grand is 4-100, Super is 8-200, Ultra is 16-300, Ultra+1 (V) is 32-400, Ultra+2 (W) is 64-500.