Check out example codes for "create user sql". It will help you in understanding the concepts better.

Code Example 1

-- Creates the login AbolrousHazem with password '340$Uuxwp7Mcxo7Khy'.  
CREATE LOGIN username   
    WITH PASSWORD = 'password';  
GO  

-- Creates a database user for the login created above.  
CREATE USER AbolrousHazem FOR LOGIN AbolrousHazem;  
GO

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