The project plan includes not only the work breakdown structure (WBS), but also the project schedule with the planning activities, their duration and completion dates, as well as cost and resource plans. All in all, the work breakdown structure should include all relevant information necessary for the successful execution of the project.
The creation of the work breakdown structure is one of the tasks of the project leader or project manager (depending on the definition of the roles in the company). The project manager then also determines the project staff who are required to perform the tasks of the project.