Managing projects is not a trivial job. You need to have the necessary skills, experience and of course the right project management tools to help you. But when it comes to managing large projects things are becoming even more complicated.
Sometimes companies need to manage large projects that extend on several years and that require a huge amount of work to be completed. This kind of projects are too big to be handled as a whole and must be decomposed in several smaller parts. Each part is treated as a separate project with its own assigned project manager and its own budget and time constraints. However all these projects are related and are actually subprojects of a master project.
The idea is that the program manager is running multiple projects and all those projects are managed by other project managers. As a program manager, you need to see a consolidated schedule view to see how the program is doing. The master project should offer the structure of the subprojects and show the dependencies between the projects. Of course resources can be shared so that overallocations and overtime costs to be detected and correctly computed.