Josh Miller, an app developer at Facebook, likens Rooms to early Web communities, like forums and message boards, which "were meeting places for people who didn't necessarily share geographies or social connections, but had something in common."
Rooms allows you to create a forum, based on interest, and share it with others. The room you create (or are involved in) is a stream of photos, text, and video populated by whoever shares to it. The one who creates the room has almost total control, too. It has something similar to Google+, as there is even a nice red plus at the bottom!
As unoriginal as Rooms may be, it's got a lot of use cases, just like those chat rooms and other social services it copies. You can have a family-only room, a community room for your neighborhood, or just one about something you're passionate about.
Facebook says Rooms will be available for sharing, and even teases a QR code method for offline sharing. It looks as though you screenshot the invite QR code sent to you, then enter a Room, which then makes the screenshot of a QR code your invitation. That makes sharing pretty personal, and gives the Room creator total control over the forum.
The app itself is free, and Facebook says that the app will feature guidelines within each individual "room" or community. If a moderator believes someone should be banned, they can be, and their device will actually be banned from that specific room indefinitely. Miller says that he's aware of the limitations that may bring, especially towards free speech, but that this method is the only way to prevent Rooms from descending into a cesspool of hatred.
Moderators, outside of banning people, will also be able to change the Room's name, as well as change the look of the community, too, from images to color schemes.
The app is currently launched for Apple devices and can be downloaded here.
For further reading, the full details can be read from from Rooms official blog post here