Learn Russian: Заказ подтверждён, вы забронировали двухместный номер. - The order is confirmed, you booked a double room.

подтверждён is a short-form past passive participle. We use short forms when they act as the main verb of the sentence (the predicate) to say that an action was done to the subject. Here, it means the order 'is confirmed.' You would use the full form подтверждённый to describe a noun directly as an adjective, like in the phrase 'a confirmed order' (подтверждённый заказ).

How is the short form подтверждён formed from the infinitive подтвердить?

For verbs ending in -ить, we drop the -ить and add -ен- or -ён- to make the participle. Because the stress falls on the end of this word, it gets the ё suffix. To make it a masculine short form matching the masculine noun заказ, we drop the final adjective endings, leaving us with just подтверждён.

I learned that номер means 'number'. Why does it translate to 'room' here?

номер is the standard vocabulary word for a hotel room in Russian! You can tell from the context of booking (забронировали) and the adjective двухместный (double) that it refers to a room in a hotel, not a mathematical number.

How is the word двухместный (double) constructed?