IMHO, you need to use Linqpad with an existing database with data in the tables and play with Linqpad to get your desired results using Linqpad and Linq queries against the database tables. This is assuming you know how to use Linq. By using Linqpad, it will help in the long run on how to use Linq.
If you are posting requirements as to what you want to do, then follow your requirements and do it.
https://learn.microsoft.com/en-us/samples/dotnet/try-samples/101-linq-samples/
https://www.tektutorialshub.com/linq-to-entities/linq-to-entities-tutorial/