First thing to do is figure out your database schema which fulfills business requirements. Next, create the database and tables along with setting up relations. Populate tables to allow writing SQL statements to validate that you can perform acts against business requirements.
Now you can start coding and would recommend all data operations are not done in the user interface but instead are in classes which the user interface calls.
Take time to refrain from creating the user interface and interact with the data, instead write out unit test and validate all operations can be performed. This way when (and it will) not writing unit test first something will not work right and now you need to figure out if it is a code problem, an external issue or something not configured properly in the user interface
Sample design for a database which will not match your requirements but is a start to see what you need to do.
I recommend using SQL-Server Express and SSMS (SQL-Server Management Studio) coupled with Entity Framework Core. Once the database is created and verified use a Visual Studio extension known as EF Power Tools to reverse engineer your database into classes/models.
At this point I have given you the steps to follow.
I did look at your PDF, between my recommendations and the PDF it's time for you to dig in and work. It's a large homework assignment and intended for you to learn.