I seriously don't get the room metaphor. It's too much of a black box.

From what I understand, it works like this:

1. You give a fixed amount, of how much you would spend max, say for Coffee at Starbucks. There is some mutlisig(that means neither you, nor the sender can do anything alone) and n-LockTime(which means you just get all back, if nothing happens)-magic. That's called a channel.
2. Now, you buy Coffee. You give Starbucks the transaction, which they don't put on the blockchain, since they know you will come again.
3. Next day, you buy another Coffee. You give Starbucks a new transaction, with money for both coffees(note, that they can not execute both transactions).
4. You realize that Starbucks is shitty coffee and never come back to them again. After a while, they see, that you are not coming back and just execute the last transaction you gave.
5. After n-LockTime is reached, the remaining money in this channel is send back to you.