The building blocks of SAP Project System

At the highest level of SAP PS, projects are defined and then structured into an organizational form that maps to the specific project.

Work Breakdown Structure
The project is first broken down into work breakdown structures (WBS) which map to specific project deliverables.

Networks
Each WBS can then be broken down into networks of activities.  A network can be thought of as a list of tasks organized into a process flow with specific timing.

Activities
Activities are the key tasks to be completed.  These activities map to internal activities, external activities, cost activities and materials components.

Work Centers
Internal activities are assigned to work centers (resources) to be completed.

A graphical  structure of the PS organization is as follows: