SQL Server :: Playing With Stored Procedure And Returning Value To Parm

I been trying to get a simple stored procedure called and get its returned value back to a parm. In this case I am trying the simplest one I can make to get it to work and the I can build form there. I have tried to do this about 100 times and I try try and say heck with it and do it with out using a stored procedure and move on but I would really like to figure this out. I created a stored procedure called ReqLineItemTotal. It looks like this

USE [OnBillPROD]
GO
/****** Object: StoredProcedure [dbo].[ReqLineItemTotal]
Script Date: 11/09/2010 14:08:39 ******/
SET ANSI_NULLS ON
GO
SET QUOTED_IDENTIFIER ON
GO
-- Author: Bill Blair
-- Create date: 11-9-2010
-- Description: ReqLineItemTotal
-- ALTER PROCEDURE [dbo].[ReqLineItemTotal]
-- Add the parameters for the stored procedure here
@SessionIDNo nvarchar(50) = 0

AS
BEGIN
-- SET NOCOUNT ON added to prevent extra result sets from
-- interfering with SELECT statements.
SET NOCOUNT ON;
-- Insert statements for procedure here select
(select SUM(dbo.TempReqDetail.Amount)
from dbo.TempReqDetail,dbo.tblReqAmountTypes
where dbo.tblReqAmountTypes.AmountType = dbo.TempReqDetail.AmountType and
dbo.tblReqAmountTypes.NumericOpperator = '+' and
dbo.TempReqDetail.SessionID = @SessionIDNo) -
(select SUM(dbo.TempReqDetail.Amount)
from dbo.TempReqDetail,dbo.tblReqAmountTypes
where dbo.tblReqAmountTypes.AmountType = dbo.TempReqDetail.AmountType and
dbo.tblReqAmountTypes.NumericOpperator = '-' and
dbo.TempReqDetail.SessionID = @SessionIDNo) AS LineItemTotal
END

From what I understand I should be getting my total back as LineItemTotal. So I want to call it pass it my parm of @SessionIDNo and have its returned value set to my @LineItemTotal parm. Trying to use these stored proc's always seems like way more work than they are worth but perhaps if I ever get the hang of it would make since to me.