Companies, both customers and vendors, may have related data in the following layouts:
Purchase Orders (vendors)
Estimate Orders (customers)
Sales Orders (customers)
This information is accessible from the company's record on the Company layout. To access this information, go to the top menu bar and click "More..."
If any related data exists, a window will appear with that information. For example, clicking the Sales button for the customer Divavu will display this:
Clicking on a particular line will navigate you to that record. For example, clicking on the second line in this list will take you to the Sales Order record SO10006.