Když chceš jít na poštu, musíš přejít most a jít dál rovně.

In this sentence, když is best understood as if:

Když chceš jít na poštu... = If you want to go to the post office...

Literally, když often means when, but in natural Czech it can also introduce a condition, especially in everyday speech. So a learner will often see it used in places where English would prefer if.

Czech usually leaves out subject pronouns when they are clear from the verb ending.

• chceš = you want
• musíš = you must / you have to

The ending -š already shows that the subject is you singular, so ty is not necessary.

You could say Když ty chceš..., but that would usually add emphasis, something like if you want...

Both are 2nd person singular present tense forms.

• chtít = to want → chceš = you want
• muset = to have to / must → musíš = you have to

So the sentence is speaking directly to one person: you.

If you were talking to more than one person, you would say:

• chcete
• musíte

Because jít is the infinitive: to go.

In Czech, just like in English, verbs such as want and must/have to are followed by an infinitive:

• chceš jít = you want to go
• musíš přejít = you have to cross
• musíš ... jít dál = you have to ... go farther / continue

So jít stays in the infinitive because it depends on another verb.

This is a very common learner question.

Both na and do can sometimes mean to, but Czech uses them differently depending on the place and idiom.

Here, na poštu is the normal expression for to the post office as a destination.

• jít na poštu = to go to the post office

With places like institutions, services, events, or activities, Czech often uses na:

• na poštu
• na policii
• na úřad
• na koncert

Meanwhile, do is often used for going into something or into a more enclosed place:

• do školy
• do banky
• do domu

You should learn jít na poštu as a fixed, natural expression.

Poštu is accusative singular of pošta.

• nominative: pošta
• accusative: poštu

After a preposition of motion like na meaning to, Czech usually uses the accusative:

• jít na poštu
• jít na stanici
• jít na zastávku

So pošta changes to poštu because it is the destination of movement.

Both ideas exist in Czech, but they are structured differently.

• přejít most = to cross the bridge
• jít přes most = to go across the bridge

In your sentence, přejít is used, so the bridge becomes its direct object:

• přejít most

This is very natural Czech.

A useful contrast:

• jít přes most focuses on the path: go over/across the bridge
• přejít most focuses on completing the crossing: cross the bridge

Most is in the accusative singular, but for this noun the accusative looks the same as the nominative.

• nominative: most
• accusative: most

That is normal for many masculine inanimate nouns in Czech.

So even though the form does not change, the case still matters grammatically.

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

• přejít = perfective → to cross, as a completed action
• přecházet = imperfective → to be crossing / to cross repeatedly / habitually

In directions like this, Czech often uses the perfective because it gives a clear instruction with a result:

• musíš přejít most = you have to cross the bridge

It means you complete that step, and then continue.

Because Czech, like English, often leaves out repeated words when they are understood.

• musíš přejít most a jít dál rovně

This means:

• you have to cross the bridge and go straight on

The second musíš is unnecessary because it clearly applies to both infinitives:

• přejít
• jít

If you repeated it, it would still be grammatical, but less smooth:

• musíš přejít most a musíš jít dál rovně

They work together to give directions.

• dál = farther / further / on
• rovně = straight / straight ahead

So:

• jít dál rovně = go farther straight ahead
• more natural English: continue straight on or keep going straight

A good way to feel the difference is:

• rovně tells you the direction: straight
• dál tells you to continue: further/on

Yes, Czech word order is fairly flexible, but the original order is natural and clear.

• Když chceš jít na poštu, musíš přejít most a jít dál rovně.

This sounds like normal spoken directions.

You can move words around for emphasis, but not every change sounds equally natural. Also, the order of actions matters:

1. přejít most
2. jít dál rovně

So the sentence presents the route step by step.

Yes. The finite verbs are in the present tense:

• chceš
• musíš

But the sentence is not really talking about what is happening right now. It is giving a general instruction or route explanation.

That is completely normal in Czech:

• Když chceš... musíš...

English does the same thing:

• If you want to get there, you have to...

So this is present tense used for a general situation, not just a single moment.

Two parts often trouble English speakers:

1. chceš The beginning chc- is a real consonant cluster in Czech.
You more or less pronounce both sounds:

• ch as in the German Bach or Scottish loch
• then ts-like c

So chceš is roughly kh-tsehsh, with one syllable at the start moving quickly into the next sound.

2. přejít The letter ř is famously difficult. It is a special Czech sound, something like a mix of r and zh. If you cannot say it yet, a plain r is a common beginner approximation.

Also remember that Czech stress is usually on the first syllable of the word:

• KDYŽ chceš jít na POŠtu, MUsíš PŘEjít most a jít dál ROVně.

That will already make your pronunciation sound much more Czech.