How is erp application built on excel?

How is erp application built on excel?

Building and ERP application in excel can be from moderate difficulty to extremely difficulty.
I will give example how the principle work because it is a lot easier to explain.
 
If you have a company that buys computer parts from major suppliers,compile computers and later sells them you need to make system that have: -Ability to manage procuring of parts.
-Warehouse is needed with accurate state of items.
-Production module needs to get parts from warehouse and turn them into final product in this case PC and put product into Warehouse on final products
-From warehouse of final products there is exit of products to buyers. When sales happens warehouse needs to reduce number of sold products.
 
For this to work you need to set up following.
-Sheet where ID of products and parts would be stored
-Sheet with ID of suppliers
-Sheet with ID of buyers
-Sheet with warehouse state (best solution is for every warehouse different sheet)
-Sheet where entry of parts would be entered
-Sheet with components list needed for final product
-Sheet Production in which you enter how much products is produced. (Made structure in a way by daily production)
-Sheet where exit of products  would be entered.
 
All this should be connected in the way when a change happens in one sheet to effect all needed parts. (example when new parts arrives and entry is made it effects state of warehouse).
It is really important for a person who is making this solution in excel to be aware of things to be done and exceptions that are possible to happen and make structure to allow those exceptions to work as needed.
 
I would be able to explain you a lot better if you have more specifically question