Bitrix24 intranet - is a private network accessible only to an organization's staff. Extranet - external users invited to your Bitrix24 intranet with limited access to your account.
Intranet vs Extranet User
Intranet and Extranet users have different access levels to your Bitrix24. Here is what external user will see after accepting an invitation to your Bitrix24 intranet (sent from extranet workgroup):
Extranet users are being invited to the particular Extranet workgroup & have access to the group tools - group Messages, Drive, Tasks, Calendar, Chat, etc.
Outside the Extranet workgroup Extranet users also have access to contacts & employees who are listed as Extranet group members:
How to invite external user to Bitrix24 workgroup
You can invite external users to your Bitrix24 workgroups only in frames of Extranet Workgroups. Go to Workgroups > Create > External Workgroup or enable option Available on extranet in workgroup settings:
Use invite employees section to add employees. Use Invite external users to add external users to the workgroup:
Extranet workgroups are marked with orange color, so that you can easily understand which groups have external users. You can also add new external users to the existing Extranet workgroup with the help of Actions tab > Invite to Workgroup.