Leadership is a unique Sailing Skill that can only obtained by completing The Black Pearl Crew Story Quest. This skill allows the pirate to recharge all of their other sailing skills at a much faster rate.
To use Leadership, you must be at the helm of your ship, and then press the 8 key or click on the Leadership icon.
Using Leadership while using another skill can make them fizzle.
Since skills can be increased up to 5 maximum, it stands to reason the developers of Pirates Online intended for there to be several more chapters - though only Chapter 1 was complete upon release and only fragments of Chapter 2 were hinted at.