You have to enter in the calendar, from Teams app.

 In the new meeting box you simply have to add the external contact e-mail, as in the image below:

Anyone outside of Kemin who attends a Teams meeting will receive a link to follow .

That will allow them to attend the meeting.

 When they attend, they will show up in a virtual "lobby" outside of the meeting. 

Whoever within Kemin has organized the meeting will get a notification that a guest is attending and needs to be allowed into the meeting from the lobby.

Please not that they have to attend with their Teams app, dial in with phone is not yet available.