You spend 1 action to charge an ability you know with the Charge trait. Choose a single ability; it gains 1 Charge Level, up to its max. You can hold charge on only one ability at a time. The ability or feature will determine its additional effects based on charge level.
You can spend multiple actions to gain multiple charges on one ability.
If you are knocked unconscious, start your turn at 0 HP, or willingly start charging a different ability, you lose all stored Charge Levels.