Question About Linking Forms & Records

Question About Linking Forms & Records

As I am trying to learn more about how to use this, I was wondering if people could point me in the right direction for something. Say I have a product that has 1000 units available for sale. Someone orders 5 units, and I now want it to display it as 995 units available. How do I do this? Do I enter it manually, or can it be done automatically?

What I do everything manually, and so I enter a record for that customer ordering 5 units. Can it automatically decrease the units available from 1000 to 995 without me having to update more than one form?

Thank you.