Imagine that you have a company and want to do your job the most efficiently. As we know each project has dozens of details and fields. Let’s compare two situations:

1. You want to build a building and you arrange only one worker for this task. This worker has to work on all the fields and this is obvious that this is not efficient way of managing the project. Because of wasting time during this period, you will also lose money.
2. In the other case, you arrange enough workers for all fields and save time and money. Before starting any project, project manager has to plan everything detail by detail and divide into different parts.

This is called WBS. A Work Breakdown Structure (WBS) is used for breaking down a project into easily manageable components, or bites. Here we'll break down the process for you, making it easy to use these structures in your project planning (1). 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.

A WBS diagram expresses the project scope in simple graphic terms. The diagram starts with a single box or other graphic at the top to represent the entire project. The project is then divided into main, or disparate, components, with related activities (or elements) listed under them. Generally, the upper components are the deliverables and the lower level elements are the activities that create the deliverables (1). 

Work breakdown structure (or WBS) is a hierarchical tree structure that outlines your project and breaks it down into smaller, more manageable portions. In Wrike, you can build a WBS by creating folders and subfolders, and can even go further to divide individual tasks into subtasks (2).

Reference

1. http://www.brighthubpm.com/templates-forms/2645-what-is-a-work-breakdown-structure/
2. https://www.wrike.com/project-management-guide/faq/what-is-work-breakdown-structure-in-project-management/