Discretionary Access Control
Discretionary Access Control (DAC) is a security implementation to restrict access to objects, such as files and directories. A user or a group of users gets access based on ownership and the permissions on the objects.
In cloud environments, user and group management is maybe not a part of your daily job. It's often delegated to Identity Management Systems such as an Active Directory (AD), and you don't need that many user accounts; authentication and authorization at an application level are more important nowadays. But it's still a good idea to be able to verify users and know how the underlying system works.
User management
If you deploy a virtual machine in Azure, in the wizard you'll specify a user, which will be created by the Azure Agent in the virtual machine—for instance, if you deploy a virtual machine with PowerShell:

You can use this account to log in. It's a normal user, also called an unprivileged user, which doesn't have administrative privileges...