In a room you can invite others by using thebutton at bottom left of screen.
This will give you a few different ways to share your room:
Room link: This will give you a URL link to the room, you can copy or tweet this link to share it with others. They simply need to visit this URL to join.
Room Code: This six digit code that expires every 72 hours. To join a room with a code, visit hub.link and type in this code.
Embed Code: (Only displayed to those with room permissions). You can use to this embed a link to your room on a webpage, remember everyone with access to the site will be able to enter the room.