Users use O365. How Can I create an Extranet site in O365 and Share with external users without adding them to AD? Thanks in advance
This is one of the best SharePoint-Features in Office365: Easy sharing of content with external users outside your organization. There is no need for an ActiveDirectory account. Users can share stuff anonymous or to any eMail-Address. If there is no Microsoft-Account registered on that Mail-Address, user must create one.
Look at this article for more details about your possibilities: