Learn Hardcore Russian: Номер, который я забронировал, находится на третьем этаже. - The room that I booked is on the third floor.

In Russian, который is the standard relative pronoun to introduce a clause that describes a specific noun—in this case номер. It must agree in gender, number and case with its antecedent (here masculine singular nominative). While you might hear colloquial speech like Номер что я забронировал…, that use of что is non-standard and should be avoided in formal or written Russian.

Why are there commas around the clause который я забронировал?

The commas mark the beginning and end of a subordinate (relative) clause. This particular clause is non-defining (it adds extra information: “the room, which I booked, …”), so it is set off by commas. If the clause were essential to identify which room you mean (defining), you would typically omit one or both commas.

Why is забронировал in the perfective past tense, and what’s the difference between бронировал and забронировал?

забронировал is the perfective past form of забронировать, showing that the booking action is completed (“I have booked”). The imperfective бронировал would emphasize the process or repetition (“I was booking” or “I used to book”), which doesn’t fit here because you want to state that the booking is done.

Why does забронировал end with -л? How would a female speaker say it?

In Russian, past-tense verbs agree with the subject in gender and number. The ending -л marks masculine singular (“I” spoken by a man). A female speaker would say я забронировала (ending -ла), and a plural subject would use -ли.

Why is the phrase на третьем этаже used? Why на and why the prepositional case?

To express “where?” (где?), Russian uses prepositions with specific cases. For floors (этаж), the convention is на + prepositional. The adjective третий (“third”) becomes третьем (prepositional singular masculine), and этаж becomes этаже.

How do ordinal numbers like третий decline in Russian?

Ordinals decline like adjectives. For третий in the singular masculine you get:
• Nom: третий
• Gen: третьего
• Dat: третьему
• Acc: третий (or третьего if animate)
• Instr: третьим
• Prep: третьем
In на третьем этаже, третий is in the prepositional case: третьем.

Why is находится used instead of есть, and can it ever be dropped?

Russian rarely uses есть (“there is”) for location. Instead you normally say находится (“is located”) or, in very informal speech, you can omit any verb in the present tense. For example:
• Formal/written: Номер, который я забронировал, находится на третьем этаже.
• Informal/telegraphic: Номер, который я забронировал, на третьем этаже.
The full verb находится makes the sentence grammatically complete and unambiguous.