If they are of INT type then you would want to convert to VARCHAR() first otherwise they will be added (as in Math addition). For example:
DECLARE @First INT, @Second INT
SELECT @First = 1, @Second = 2
SELECT CONVERT(VARCHAR(50), @First) + CONVERT(VARCHAR(50), @Second)
Or you could use CONCAT()
SELECT CONCAT(@First, @Second)
which will convert them to strings for you.