Questions: 
 
1) What is WBS element? 
2) What is the Tcode to get to that screen? 
3) What is the need and purpose of WBS element? 
4) Do we happen to work on Functional module during our implementation project? 
5) In what scenario/situation we will be working on WBS? 
 
By Raju:
 
WBS is nothing but Work Breakdown Structure. It is mainly used in Project System (PS) module. Tcode : CJ20N 
 
For any project defined we must have at least one WBS. Within this WBS we can have networks. Networks are nothing but the series of activities. Material are used to perform the activities. 
 
To explain in detail just consider one example: 
 
Govt of India wants to have Roads to be build throughout India. So Project can be defined in sap as "Connectivity".  WBS can be roads within different states like Roads for Gujarat, Karnataka etc.. i.e. WBS Gujarat, WBS Karnataka etc. 
 
We can define different networks for these WBS like Road Between Ahmedabad to Surat or Between Bangalore to Belgham.   For this network we can have many activities like Land selection, Land Preparation, Road Building, Final finishing etc. 
 
A good example:  Project Systems comes into play only when the industry's business is based on projects like. Construction companies, Engineer to Order scenarios. You may not see anyone using PS module for retail business. As explained, you have a main project which is broken down into WBS elements. You can use the TC CJ20N to create the project and the WBS elements. Each WBS may have multiple Networks associated and each Network may have multiple Network Activities as explained in the example by Hemal. 
 
On the Sales Order, if your client is implementing PS module, you may have to attach the Sales Order to the WBS element it belongs to. WBS element is nothing but a bucket where all the activities belonging to that particular part of the project are captured. In the example, WBS Gujurat will tell you how many Sales Orders were created for the Gujurat sector, how much was spent on raw materials, what's the correct stock (project stock) available. How many Production Orders have been confirmed and how many of them are getting confirmed in the future. How many invoices have been generated or how much revenue has been generated for that particular sector. How many deliveries have been made, what deliverables are still not accomplished. 
 
So as you can see, PS is the center stage for all the modules that are being implemented like FI/CO, SD, MM, PP in this example. You can have cost centers and work centers defined. You can also have profit centers assigned at the plant level and get reports on various selection criteria. 
 
In a complete cycle of PS, like in reality, you initiate a project, you confirm/release the WBS/activities as per requirement, you execute the project and you close it. 
 
One cannot initiate an activity unless it has been released by the project manager. Everything is accountable here and every dime is counted and at the end you know how much did you spend or make on each sector (WBS). Don’t get confused with the term sector here as I am using it just for the explanation purposes.  
 
In one typical example, the company I was working with until not too long ago, had Deliveries from the Project (TC: CNS0). We never used VL01N. We used CNS0 to create a delivery and then used VL02N for confirming the picking quantity for the already created delivery document. 
 
Try going to CJ20N and you will know more about it.

Get help for your SAP PS problems
SAP PS Forum - Do you have a SAP PS Question?

SAP Project System Books
SAP PS Books - Certification, Interview Questions and Configuration

SAP Project System Tips
SAP PS Tips and Project System Discussion Forum

Best regards,
SAP Basis, ABAP Programming and Other IMG Stuff
http://www.erpgreat.com