Configuring A Database In Sqlserver?

I am learning dotnet thru Microsoft Official Curriculum and I got stuck up at one point. That is I couldn't configure the required databases according to the sql server I have installed and configured. I created a doctors database and while configuring using the below code I couldn't know what is 'ASPNET' in "SELECT @s = @@servername + 'ASPNET'"
Also what is 'webuser'



---Configure Doctors
USE doctors

GO

DECLARE @s varchar(50)
SELECT @s = @@servername + 'ASPNET'
EXECUTE sp_grantlogin @s

EXECUTE sp_grantdbaccess @s, 'webuser'

GO

GRANT EXECUTE ON [getUniqueCities] TO webuser
GRANT EXECUTE ON [getDrSpecialty] TO webuser


GRANT SELECT ON [specialties] TO webuser
GRANT SELECT ON [doctors] TO webuser
GRANT SELECT ON [drspecialties] TO webuser

GO


Can anyone help me how to solve my problem?
Your help would be very much appreciated

Thanks and Regards

Kavitha