Create active directory user on SQL Server
If an active directory user can't access a database you might see:
Login failed for user 'MYDOMAIN\MYUSER'.
If the user has never accessed any database on that server, then a DBA needs to created the login at a server level first, e.g.:
USE [master]
GO
CREATE LOGIN [MYDOMAIN\MYUSER] FROM WINDOWS WITH DEFAULT_DATABASE=[master], DEFAULT_LANGUAGE=[us_english]
GO
A DBA can then create the user on the specific database with this command:
USE [TheSpecificDatabase]
GO
CREATE USER [MYDOMAIN\MYUSER] FOR LOGIN [MYDOMAIN\MYUSER] WITH DEFAULT_SCHEMA=[dbo]
And can then grant db_owner role with:
ALTER ROLE [db_owner] ADD MEMBER [MYDOMAIN\MYUSER]
Or with:
EXEC sp_addrolemember N'db_owner', N'MYDOMAIN\MYUSER'
If uncomfortable with db_owner you might consider db_datareader instead.