How to insert a stored procedure data into a column of an existing table SQL server

Hello,

I created a stored procedure in ms sql server. The stored procedure subtracts two columns in the same table. How do I insert this stored procedure data into the Inventory column of an existing table dbo.Store? The stored procedure is:

ALTER PROCEDURE [dbo].[sp.StoreBilling]
	
AS
BEGIN
	SET NOCOUNT ON;

DECLARE @Stock decimal(10,2)=0.00
DECLARE @Spoilage decimal(10,2)=0.00

SELECT A.Stock, A.Spoilage, A.Stock-A.Spoilage AS Inventory
FROM dbo.Store AS A
END

What I have tried:

ALTER PROCEDURE [dbo].[sp.StoreBilling]
	
AS
BEGIN
	SET NOCOUNT ON;

DECLARE @Stock decimal(10,2)=0.00
DECLARE @Spoilage decimal(10,2)=0.00

SELECT A.Stock, A.Spoilage, A.Stock-A.Spoilage AS Inventory
FROM dbo.Store AS A
INSERT INTO  dbo.Store
OUTPUT Inventory
VALUES(@Stock-@Spoilage); 
END

Error message: 
Msg 213, Level 16, State 1, Procedure sp_StoreBilling, Line 20 [Batch Start Line 7]
Column name or number of supplied values does not match table definition.

Tags: SQL