Good morning. As a member of the team that created the two modern Northwind sample databases, I can assure you that you will not be an expert after exploring the Northwind database applications.
It was never our intention to make anyone an expert, nor would it even be reasonable to suggest that is possible with a single template. Templates like Northwind Starter and Northwind Developer are showcases for features, methods and design principles that underlie good database design.
That said, you WILL have a solid starting foundation from which to build your skills, knowledge and understanding of Access and Access database development. And that is the important point.
You will find documentation here:
https://support.microsoft.com/en-us/office/northwind-2-0-developer-edition-32eb79d2-bede-4ea4-b575-0714ca8dc1e2
Among other things, you'll see tables designed to satisfy basic Database Normalization.
You'll see good patterns for form and report design.
You'll see good patterns for VBA coding.
However, it is also important to recognize Northwind is a single business model, and not a universal database design.
Northwind is a fictitious trading company whose customers are independent grocery stores.
Customers call in orders or place them over the internet. In this template, Internet orders are a mockup.
- Northwind invoices, ships, collects payments, and closes orders. Purchase orders and inventory management are also included in this edition.
Other business models will require their own specific features and functions. What Northwind will do is provide you a base from which you can work, but which will need to be adapted to whatever business model you need for your own projects.
It's a great starting point. Good luck.