What does "-X Cost" mean on a Growth option or Power threshold?

What does "-X Cost" mean on a Growth option or Power threshold?

It means you have to pay that much Energy to pick that Growth option or use that level of your Power. [B&C p. 15, JE p. 11]
If you don't have the Energy, you can't pick that Growth option. If you don't have or don't want to pay the Energy, skip over that Power level and continue resolving the rest of the Power.