For my simple app, I added a new setting named ITworldConn, changed the Type to (Connection String), and Scope to Application. To finish your new connection setting, click the small ellipsis button.

If you just want to get going with a code-first database, you don't even need to define a connection string -- just write your objects.

Take advantage of the open source library Serilog to log your ASP.NET Core application’s data to SQL Server or another database target.