Room Mailboxes are often used to resereves rooms for meetings, trainings, by using Outlook`s Calendar.
In order to create a Room Mailbox, you have to open Exchange Management Console, go to Recipient Configuration, right click on Mailbox and select New Mailbox..
In the next window, select Room Mailbox and click Next.
For the next step, you can either select an existing user(if you already created one for the specific room), or create a new one, which is usually the case. If you go with new user, fill all the necessary filds (name, account, email address) and don`t forget to choose an Oraganisational Unit for it. For the following windows, you can click next, since you don`t have to make any additional settings for it to work.
You can then find the new Room in your outlook calendar, by searching for it by its name