How to populate related tables?

Question

SQL Server

Hello! I can not figure out the principle of filling tables with foreign keys. Errors keep popping up.
How, for example, to fill in the sales table if its fields are linked to another table?

Answer 1

First fill in the Products.
Then fill in Buyers, Sellers.
Then fill in Sales.
How are sellers and buyers connected?
The general principle is first what is a directory, then what refers to it.