To create a Room in TM3 web select the Settings icon in the top right area of the interface.
Next select the Setup drop-down, choosing Rooms.
Once you arrive here it will show you all the rooms currently assigned to TM3.
To add a new room click on the blue Add button.
This brings up the screen below. You enter the description (name of the room), choose the location (where the room is registered) and can also choose a colour (This can help you easily identify between multiple rooms).
Once you fill in the details click Create.
Once the rooms have been created, you will see them within the Room Manager pane.
Now your new room appears in the diary as shown in the image below.