Concatination is the process of joining character strings end-to-end.
select u.userid,hrms.FirstName+'('+hrms.EmployeeCode+')' as employee from [dbo].[User] u inner join hrmsemployee hrms on hrms.EmployeeID=u.employeeid
SELECT CAST(11 AS VARCHAR(10)) + CAST(33 AS VARCHAR(10)) +CAST(99 AS VARCHAR(10)) AS TrueResult output 113399
SELECT 11+33+99 AS WrongResult output 143
select u.userid,concat(hrms.FirstName,'(',hrms.EmployeeCode,')') as employee from [dbo].[User] u inner join hrmsemployee hrms on hrms.EmployeeID=u.employeeid
SELECT CONCAT(11,33,99) AS Result output 113399