Inviting other participants is very easy: when you are in the room, click the icon in the top right corner of the room. A box pops up on the left, where you can type the email address of the person you would like to invite.
Click "Add" to add them to the recipient list. If you would like to invite multiple persons at once, keep adding their addresses.
Once you are finished, click "Send Invitation" to send the invitations out via email. The participants will receive an invitation, which will allow them to join.