The default scope tag is automatically added to all untagged objects that support scope tags.
https://learn.microsoft.com/en-us/mem/intune/fundamentals/scope-tags
The company portal helps users manage their device and apps, as the administrator you can manage the company portal
https://learn.microsoft.com/en-us/mem/intune/user-help/using-the-intune-company-portal-website
This will go in detail about using the ICD tool to create provision packages for AAD join.
https://learn.microsoft.com/en-us/windows/configuration/provisioning-packages/provisioning-packages
You will need to check your role assignment and subscription service to perform some of these actions.