Gale's basic abilities have no cost to use them and they are only limited by cooldowns. The resource that's tracked in his secondary resource bar is the mechanic: Flow.
Gale can have up toFlow. Gale generates 3% of his maximum flow per auto attack. Flow does not generate or deplete idly.
Gale's ultimate is the only ability that requires flow to use. Upon reaching 100% Flow, Gale can use his ultimate. While his ult is active, Flow cannot be generated or depleted by his abilities and auto attacks, except for the over-time depletion from his ultimate.