Create an Open Teams meeting room

Create an event in your Outlook Calendar. Invite yourself. (This allows you to add the “teams” room.) 

After you “send” that invite you will see your teams meeting appear on your calendar that you can double click on. 

You can then choose to enter the room (for me its easer to setup the room when your inside it). 

Go under “More Actions > Meeting Options. 
Determine if you want to use the Lobby option or not and setup what permissions you want your guests to be able to have.

Choose “Save”

Choose “More Actions > Meeting Info”

Choose the “Copy Join Info" button at the bottom of that window
That will copy the connection information you can paste into an email to give to your guests.