Hello, I am attempting to make a stock number using a barcode scanner.

I know that there is a similar thread, but I do not understand anything, so can someone please explain in a more simple way?

The difference is when I scan items, the count goes up automatically, I don't mind to make 3 columns with one that goes up and the other goes down and the third one is total.

Feel free to ask any specifications, but I might not understand the question. Thank you!