Where to enter the key from Skype for business?

Question

Skype

Received as a gift several keys for "Skype for business".
Question: how to use them? Where to enter?
And what kind of e-mail should be entered in the "Login address" field (corporate login address, but not a Skype login and not even a Microsoft account)?

As I understand it, you need to attach one of the donated codes to this very e-mail.
On the microsoft website, they only write about logging in "Skype for business" to Office 365 and 2016,
and, it seems, the login address must be from the account of one of the Offices.
But our institution does not have these offices, and therefore it is not clear how to use the keys from "Skype for business"...