The Discipline of Leadership is about motivating and organising people. The Tests are largely designed so that in order to pass, you must have the support of people that will not personally gain from your passing (in contrast to Worship where everyone gains from helping). A good Leader is a friend to many and often involved in many projects.
The Discipline is sometimes referred to as the Discipline of Popularity, which is certainly a factor, but there is more to it. Leadership is also often displayed in many ways by people that are not followers of the Discipline.
Details on the Tests of Leadership may be found on the Tests page and the rewards of advancing in the Discipline on the Leadership Rewards page.
Useful pages: