Stored Procedure with both input and output parameters

Store Procedure

CREATE PROCEDURE [dbo].[GetPermission]
    @userName varchar(50),
    @permission int output
AS
BEGIN

    select @permission = PERMISSION from USERS where UserName = @userName

END;

EDIT:

another option is create a function instead, example:

CREATE FUNCTION [dbo].[GetPermission](@userName [varchar(50)])
RETURNS [int] 
AS 
BEGIN

    declare @permission int

    select @permission = PERMISSION from USERS where UserName = @userName

    return @permission

END;