Is there a way to use users in an Azure Active Directory as users for an Azure Virtual Machine?
Respectively, is there a way to create multiple user accounts for an Azure Virtual Machine?
No, you can't use AAD to store logon information for VMs.
If you need central authentication for Windows VMs in Azure, do what you would do on-prem. Create a new Active Directory domain using one or more VMs as domain controllers and join your other Azure VMs to the domain.
If you already have AD on-prem, you can extend it across a site to site VPN or ExpressRoute rather than creating a whole new AD domain. Best practices are here: http://msdn.microsoft.com/en-us/library/azure/jj156090.aspx
Alternatively, you could always just create local user accounts if you only need a small number of logins for a small number of servers.
If you use Windows 10 Pro, Education or enterprise edition (images are available for MSDN subscribers), you can use Azure AD user to log to these VM.
To do that, you need to Azure Active Join your Windows 10 VM. http://blogs.technet.com/b/ad/archive/2015/05/28/azure-ad-join-on-windows-10-devices.aspx
Note : this feature is not available for Windows Server OS.
Azure AD Domain Services may be an answer the you first question: https://docs.microsoft.com/en-us/azure/active-directory-domain-services/active-directory-ds-admin-guide-join-windows-vm-portal and https://docs.microsoft.com/en-us/azure/active-directory-domain-services/active-directory-ds-getting-started
For your second question, creating local user accounts is as simple as using this command in an elevated command prompt :
net user username password /add
If the user needs to be an admin:
net localgroup Administrators username /add