The Work Breakdown Structure Document

The WBS is designed to help break down a project into manageable chunks that can be effectively estimated and coordinated. Some widely used reasons for creating a WBS include:

Assists with accurate project organization
Helps with assigning responsibilities
Shows the control points and project milestones
Allows for more accurate estimation of cost, risk and time
Helps explain the project scope to stakeholders

A work breakdown structure is just one of many project management forms.
To start out, the project manager and subject matter experts determine the main deliverables for the project. Once this is completed, they start decomposing the deliverables they have identified, breaking them down to successively smaller chunks of work.

"How small?" you may ask. That varies with project type and management style, but some sort of predetermined “rule” should govern the size and scope of the smallest chunks of work. There could be a two weeks rule, where nothing is broken down any smaller than it would take two weeks to complete. You can also use the 8/80 rule, where no chunk would take less than 8 hours or longer than 80 hours to complete. Determining the chunk size “rules” can take a little practice, but in the end these rules make the WBS easier to use.

Regarding the format for WBS design, some people create tables or lists for their work breakdown structures, but most use graphics to display the project components as a hierarchical tree structure or diagram.