Get Current Month Total Sales Using SQL Query or Store procedure, get Today Date from SQL , Get first Day of the Month

CREATE PROCEDURE [dbo].[GetSalesbyMonthly]

AS

BEGIN

DECLARE @Today DATE;

DECLARE @FirstDay DATE;
    /*Get First Day  And Month And into @FirstDay Variable */

    SET @FirstDay= (select dateadd(dd,-(day(getdate())-1),getdate()) )
    /*Get Today And Store into @Today Variable */

    SET @Today= (SELECT CONVERT(DATE,GETDATE()) AS Today)   

    BEGIN

            SELECT  ISNULL(SUM([TotalSale]),0) AS TotalSales FROM YOURSALE TABLE  WHERE  (DATE-COLUMN BETWEEN @FirstDay AND @Today)

    END   

END