You can use SQL Server Authentication for logging into your configuration database.
SQL Server supports both Windows Authentication and SQL Server Authentication. SQL Server Authentication is where you authenticate by providing the details of a user account configured within the SQL Server.
By default an installation of SQL Server has a pre-configured SQL Server user called sa. The instance of SQL server installed with Flow (<computername>\FLow) has the sa password set as F1owsq1!
It is recommended that you change the default password to something a little more secure!
You can add further SQL Server user accounts through the Microsoft SQL Management Console
These SQL Server user accounts are often referred to as database users. Applications built on top of SQL server will often have their own users (application users), however when configuring the connection to the database you would use the database user when asked for a username and password.