There is a thread with video tutorials, but it's not updating very regularly.
If by leaders, you mean leaders of the planets, then you go to the officers window, and in the middle left, there is a list of officers. Directly above that, there is a drop down menu. Click on Civilian Administrators, and there will be a list of leaders you can elect. When you select one, you can see what they affect in the top right corner. One might improve Terra-forming by 20% and Mining by 10%, for example. Directly to the right of the list of people, there will be a list of colonies. Choose a colony you want to assign the administrator to, then click assign, which is down at the bottom. Make sure that the administrator's level is equal to or higher than the level of the colony.