There are a few things to do first. (This is over simplified but may get you started):-
• Select Manage>Database from the File menu and click the "Relationships" Tab. This is where you must define each relationship in your supply chain by dragging between the Table Occurrences to link the primary and foreign keys.
• Add Portals to your layouts. Each portal can display a related table's records and fields as rows and columns in the portal on the layout.
You need to create the relationship the lets Filemaker Pro know how they are connected. What is the connecting field from one table to another.
Customers show on invoices. Product shows on invoices. Vendors show on purchase orders. Products show on inventory.
There are natural relationships. But, if you want to relate every table to every other table, have a global field with a contant (i.e. 1) in every table and related everything on that field.
Is that good database design? I am not sure. Will it work? Yes.