That's pretty easy stuff to do. If you know the very basics of stored procedure then you should be able to do this. Also note that "What I have tried" is for showing what you have tried so far so that we can suggest a quick solution.
You may need something like following-
CREATE PROC SaveDrug
(
@DrugId INT,
@DrugName VARCHAR(50)
)
AS
BEGIN
INSERT INTO Drugs
(DrugId, DrugName)
VALUES(@DrugId, @DrugName)
INSERT INTO Stock
(DrugId, DrugName)
VALUES(@DrugId, @DrugName)
END
Hope, it helps :)