This Extended service request will initiate a process to create a federation with an external Skype/Lync server. Basically, Federation will allow your Skype/Lync users to contact other Skype/Lync users outside of your organization.

Upon placing this request you will have to enter the federated domain, certificate type and FQDN (Fully Qualified Domain Name) of the server you would like to have federation with. This information should be obtained from the owner of the domain in question.

Aside from the Extended Service request, you will need to create SRV record for your domain as described in the What Is Skype For Business/Lync Federation? article.