The meter
Your power meter fills as damage is dealt in fights you are part of, both given and taken. Each star is worth 9,000 funds of damage. When it is full enough, use the Power or the stronger Super Power from the menu.
While a power is on, all your units also get +10% attack and defence. Each use makes the next one cost more.
Picking a commander
Every commander has a day-to-day effect too. The Commander chart shows their attack and defence for every unit, and the Tier lists show how strong each is in each kind of game.