When you are in your room tap on the 'people' icon on the top right of the screen (it looks like 2 people).

Now tap on the green 'invite pals to room' selection.  Choose the pals you want to invite to the room and then tap on 'invite'.  Your pals will get an invitation to the room and when they accept they will be joined into the room.

'Swipe' the list to the right to hide it when you are finished.