Nejdřív musíme vybalit krabice s knihami a dát je do pokoje.

Nejdřív means first, at first, or first of all in this context.

Yes, Czech has a few common alternatives, such as:

• nejdřív
• nejprve
• napřed

They are often interchangeable in everyday speech, though nejdřív and napřed can sound a bit more conversational.

Because Czech often drops subject pronouns when they are clear from the verb form.

Here, musíme means we must / we have to. The ending -me already tells you the subject is we.

So:

• musíme = we must / we have to
• my musíme = we have to with extra emphasis on we

In a neutral sentence, leaving out my is completely normal.

Because they follow the modal verb musíme (we must / we have to).

After modal verbs like muset, Czech uses the infinitive, just like English does:

• musíme vybalit = we have to unpack
• musíme dát = we have to put

So the structure is:

• musíme
  • infinitive
• we have to
  • verb

This is about aspect, which is very important in Czech.

Here, vybalit and dát are perfective verbs. They present the actions as complete, finished actions:

• vybalit = to unpack completely
• dát = to put/place as a completed act

That fits the sentence well, because it describes a sequence of tasks to complete:

1. unpack the boxes
2. put them in the room

If you used the imperfective forms vybalovat or dávat, it would sound more like focusing on the process, repetition, or an ongoing action.

Here krabice is plural accusative: boxes.

The noun krabice has these relevant forms:

• singular nominative: krabice = box
• singular accusative: krabici = box (as an object)
• plural nominative: krabice = boxes
• plural accusative: krabice = boxes (as objects)

So in this sentence, vybalit krabice means to unpack boxes.

A learner might expect a special plural ending, but for this noun, the plural accusative looks the same as the plural nominative.

Because the preposition s meaning with requires the instrumental case.

The noun knihy (books) becomes knihami in the instrumental plural:

• knihy = books
• s knihami = with books

So:

• krabice s knihami = boxes with books / boxes containing books

This is a very common Czech pattern:

• stůl s lampou = table with a lamp
• taška s oblečením = bag with clothes
• krabice s knihami = box/boxes with books

Because do always takes the genitive case.

The noun pokoj (room) changes like this:

• nominative: pokoj
• genitive: pokoje

So:

• do pokoje = into the room

This is used for movement toward/into a place.

Compare:

• je do pokoje = them into the room → movement
• v pokoji = in the room → location

That difference is very important in Czech.

Je here means them.

It is the accusative plural pronoun, referring back to something already mentioned. In this sentence, it most naturally refers to krabice (the boxes):

• dát je do pokoje = put them in the room

So the full idea is:

• unpack the boxes with books
• put them in the room

Yes, it can be slightly ambiguous without context.

Grammatically, je could refer to:

• krabice = the boxes
• knihy = the books

In real context, listeners usually understand it from the situation. But if you want to be completely clear, Czech can repeat the noun:

• ... a dát krabice do pokoje = ... and put the boxes in the room
• ... a dát knihy do pokoje = ... and put the books in the room

So the original sentence is normal, but context matters.

Because that is the normal Czech order here: verb + short pronoun + place.

So:

• dát je do pokoje

is natural and standard.

The pronoun je is a short unstressed form, and Czech short pronouns usually do not stand at the very beginning of their clause. That is one reason why je dát do pokoje would sound wrong here.

Czech word order is flexible, but short pronouns follow special placement rules, and this sentence follows them naturally.