How to add parameter in rdlc report?

Question

Hello, in my RDLC report I need to show the SUM at the end of one column. For example

NAME  |  AGE  |  SALARY

 

 

 

............................................

                           @Sum_Salary

For this I go to "Report Data" -> Parameter -> Add new parameter

 

Here I did not know how to write query and where I write. I am using Visual Studi 2013.

 

Please help.