If you've subscribed to any Microsoft online service, such as Azure or Office 365, you will get the free Azure AD version along with it. It has limited features:

• Directory objects
• User/group management (add/update/delete), user-based provisioning, and device registration
• Single sign-on (SSO)
• Self-service password change for cloud users
• Connect (sync engine that extends on-premises directories with Azure AD)
• Security/usage reports