Your company administrator does it from the portal, in the Administration section:

1. Create the user with their name and email address.
2. Assign the extension and the permissions: which modules they see and which reports they can consult.
3. Send them the app activation link.

If you need more licenses than the ones you contracted, the portal tells you and it is adjusted on the next bill.

When someone leaves the company, the administrator deactivates the user: the extension stops ringing, the app on that computer loses access, and the history is kept for the company.