Getting relationship and links between tables of sql database from vb.net

I am really new to the world of vb.net and sql server, I was learning about these fantastic platforms for building an inventory application.

I want some basic and beginner help regarding setting up relationships between tables and fetch relevant information, suppose i have five tables in my sql database

1) TBLCUSTOMERS - Columns are (CustomerID, CustomerName)

2) TBLSUPPLIERS - Columns are (SupplierID, SupplierName)

3) TBLPRODUCTS - Columns are (ProductID, ProductName)

4) TBLPURCHASE - Columns are (PurchaseID, PurchaseReference, ProductName, SupplierName, Quantity, Rate, Total)

5) TBLSALES - Columns are (SalesID, SalesReference, CustomerName, ProductName, Quantity, Rate, Total)

Now i want that when i run a query to search that which product a customer bought and some other queries like this.

Can someone post a link to some beginner tutorial where i can get information to solve my problem with regards to learning the basics.

Thanks in advance