How to use STUFF keyword in Microsoft SQL Server

Usage of STUFF in Microsoft SQL Server 

General syntax of STUFF in SQL Server is 

STUFF ( character_expression , start , length , replaceWith_expression )

You can refer the details from below link
http://msdn.microsoft.com/en-IN/library/ms188043.aspx

SELECT DISTINCT COMMISION_NUMBERS = 
STUFF((Select ','+COMMISION_NUMBER from MARS_ALLOCATION_DATA where MONTH='JUN' and YEAR=2014
 FOR XML PATH('')),1,1,'') FROM MARS_ALLOCATION_DATA