Please set your database connections string in Web/appsettings.json
To create the database, you'll need to run Update-Database from the Package Manager
I tend not to use comments as I feel that the code should be easy to understand on it's own. If the code needs comments, it's too complicated!
In a real-world system, I would add validation to the CSV import to check that the file is indeed a CSV file and is in the correct format.
Many thanks, Jonathan