Query to get the Department along with their Users (comma seperated)

 SELECT 
	DISTINCT D.DepartmentName, 
	(SELECT FirstName +',' FROM  [Amatya].[dbo].[tblUsers] WHERE DepartmentId = D.DepartmentId FOR XML PATH(''))
	FROM[Amatya].[dbo].[tblDepartments] D

Result Demo:

i.e Software | Amatya,Urvi,Shryansh,Ram,Mayank

Thanks.