What is the Get Energy screen?

This screen provides a couple of options for you to regain Energy.

You can either spend 100 Gold to completely refill your Energy bar, or watch an advert to get 2 Energy (or 1 Energy in PvP) for free.

Note that you will also be taken to the Get Energy screen when you try to start a Mission when you don't have enough Energy.

Also, note that PvP mode uses different Energy than Campaign mode.