Перед тем как заселиться, нужно показать паспорт и подписать договор.

It means before or before doing something.

More literally, it is something like before that, how/when..., but in normal English you should just think of it as a fixed expression meaning before when it introduces an action:

• Перед тем как заселиться... = Before checking in / before moving in...

It is very common in Russian when one action happens earlier than another.

Because перед normally requires the instrumental case, and тот changes to тем in the instrumental singular.

So:

• тот = that
• перед тем = before that

In this expression, перед тем как functions as a set phrase, so it is best learned as a whole.

Заселиться is a perfective reflexive verb meaning to move in, to check in, or to settle into a place.

Here is the breakdown:

• селиться = to settle in, to move in, to take up residence
• заселиться = to move in/check in completely, with focus on the completed action
• заселить without -ся usually means to populate or to place someone into a room/building

So:

• заселиться = to check in / move in oneself
• заселить кого-то = to check someone in / accommodate someone

The -ся shows that the subject is the one moving in.

Because the sentence is talking about a single completed action that must happen later, after some other required steps.

The idea is:

• first: show your passport and sign the contract
• then: check in / move in

Perfective verbs are often used for one-time actions seen as complete. Here заселиться is the event that has not happened yet, but is viewed as a whole completed result: to successfully check in.

Нужно is an impersonal word meaning it is necessary, one must, or you need to.

So:

• нужно показать паспорт и подписать договор = it is necessary to show a passport and sign the contract

There is no explicit subject like you in the Russian sentence. Russian often leaves it general and impersonal where English would say:

• you need to...
• one must...
• it is necessary to...

All of those are close in meaning.

Because they describe single completed actions:

• показать паспорт = to show the passport
• подписать договор = to sign the contract

The sentence is about requirements that must be fulfilled before checking in, so the completed result matters:

• the passport must be shown
• the contract must be signed

If you used the imperfective forms показывать or подписывать, the meaning would shift toward process, repetition, or a more general activity, which is not the main point here.

They are in the accusative case because they are direct objects of the verbs:

• показать что? → паспорт
• подписать что? → договор

However, for inanimate masculine nouns, the accusative singular often looks exactly like the nominative singular.

So:

• nominative: паспорт, договор
• accusative: паспорт, договор

The case is accusative by function, even though the form does not visibly change.

Yes. The subject is understood, not stated.

In context, it means something like:

• Before checking in, you need to show your passport and sign the contract.

Russian often leaves out the subject when the meaning is general or obvious from context. The sentence sounds natural and formal this way, especially in instructions, rules, or administrative language.

Yes, Russian word order is flexible, though some versions sound more natural in certain contexts.

The original sentence:

• Перед тем как заселиться, нужно показать паспорт и подписать договор.

is a very natural neutral version.

You could also say:

• Нужно показать паспорт и подписать договор перед тем как заселиться.

This means the same thing, but the original puts stronger focus on the before checking in part first.

So the word order can change, but the original is a standard and clear way to express the idea.

They are similar, but not always identical.

• заселиться often means to move in / check in, especially into a hotel, apartment, dormitory, or room
• поселиться often means to settle somewhere, take up residence, or stay somewhere

In many contexts they overlap, but заселиться is especially common when talking about the act of entering accommodation and being assigned a place.

So in a hotel or rental context, заселиться is very natural.

Yes, it sounds fairly neutral to formal, and very suitable for:

• hotel instructions
• rental agreements
• office or administrative communication
• official notices

The use of нужно, показать паспорт, and подписать договор gives it an impersonal, instructional tone.

In everyday spoken Russian, someone might also say something more direct, such as:

• Перед заселением нужно показать паспорт и подписать договор.

That is also natural and means almost the same thing.

A helpful stress guide is:

• Перед тем как засели́ться, ну́жно показа́ть па́спорт и подписа́ть догово́р.

Key stresses:

• засели́ться
• ну́жно
• показа́ть
• па́спорт
• подписа́ть
• догово́р

A learner should be especially careful with договор: the standard stress is догово́р, not до́говор.

Yes. Russian has several ways to express before.

For example:

• Перед тем как заселиться...
• Перед заселением...

Both can mean before checking in.

The version with перед тем как + infinitive is a full clause-like structure and is often very clear for learners.

The version with перед + verbal noun is more compact and often sounds a bit more formal or administrative:

• Перед заселением нужно показать паспорт и подписать договор.

Both are correct and natural here.