A room is simply a conversation with a name. (Please note: Rooms can only be created from conversations with 2+ people). First, create a conversation or open an existing conversation, then select the settings icon at the top right of the conversation window:

Fill in the "Title" field to name the conversation:

*All new rooms will appear in the Rooms view in the sidebar (the one with the A-Z icon).

Note: direct conversations (i.e. conversations between you and one other person) are an exception as they cannot be made into a room.