How to sum a column?

Hello !
Please HELP ME!

CREATE PROCEDURE Something
@Date1 smalldatetime,
@Date2 smalldatetime,
@My_Sum decimal output
AS
Select * from Table1 where MyDate >= @Date1 and MyDate <=@Date2
set @ My_Sum = select sum(My_Sum)
exec Something My_Sum output

How to make my procedure to return all records which dates are between date1 and date2 and to sum the column My_Sum for these dates