Čím dřív půjdeme na poštu, tím méně lidí tam bude.

It is a very common Czech pattern meaning the ... the ..., just like in English comparative sentences.

So:

Čím dřív půjdeme na poštu, tím méně lidí tam bude.
= The earlier we go to the post office, the fewer people there will be.

You can think of it as:

• čím dřív = the earlier
• tím méně = the fewer / the less

This structure is called a comparative correlative in English grammar.

Dřív means earlier or sooner here.

It is the comparative form of brzy / brzo (early, soon), although in practice learners often just memorize dřív / dříve as the common word for earlier.

So:

• brzo / brzy = early, soon
• dřív / dříve = earlier, sooner

In this sentence, čím dřív means the earlier.

Yes, in this sentence they mean the same thing.

You could say:

• Čím dřív půjdeme na poštu...
• Čím dříve půjdeme na poštu...

Both mean The earlier we go to the post office...

The difference is mostly style and register:

• dřív = more common in everyday speech
• dříve = a bit more formal or bookish

Because Czech normally separates the two parts of the čím ... tím ... structure with a comma.

So the sentence is divided into:

• Čím dřív půjdeme na poštu,
• tím méně lidí tam bude.

This is standard Czech punctuation.

Because Czech uses different prepositions depending on the kind of destination, and with places like pošta (post office), Czech commonly says jít na poštu = to go to the post office.

So:

• jít na poštu = go to the post office
• být na poště = be at the post office

This is one of those combinations you mostly have to learn as a set expression.

Because after na when it expresses motion toward a destination, Czech uses the accusative case.

The dictionary form is:

• pošta = post office

But after na with movement:

• na poštu = to the post office

So poštu is the accusative singular form of pošta.

Yes. Půjdeme means we will go.

It is the 1st person plural future form of jít (to go on foot / to go).

So:

• jdu = I go / I am going
• jdeme = we go / we are going
• půjdeme = we will go

In this sentence, the action is in the future, so půjdeme is the natural choice.

Because after words like méně (less, fewer), Czech usually puts the following noun in the genitive.

So:

• lidé = people
• lidí = of people / people in genitive plural

That is why Czech says:

• méně lidí = fewer people

This is a very important pattern. Similar examples:

• hodně lidí = many people
• málo času = little time
• více peněz = more money

Because the subject here is not a simple plural noun like lidé by itself. It is the quantity expression méně lidí (fewer people), and Czech often treats this kind of expression as grammatically singular.

So Czech says:

• Méně lidí tam bude. = There will be fewer people there.

This is very normal Czech. Similar patterns appear with other quantity expressions too.

Tam means there.

So:

• tam bude = will be there

It tells you where the people will be: at that place, understood from context as the post office.

The sentence could technically still be understandable without tam, but tam makes the location explicit and sounds natural.

The basic structure čím ..., tím ... should stay, but Czech word order is fairly flexible.

This sentence is very natural as written:

Čím dřív půjdeme na poštu, tím méně lidí tam bude.

You may also hear slight variations depending on emphasis, for example moving tam:

• Čím dřív půjdeme na poštu, tím tam bude méně lidí.

That also works, but the original version is very straightforward and natural.

A fairly literal breakdown is:

• Čím = by how much / the more that
• dřív = earlier
• půjdeme = we will go
• na poštu = to the post office
• tím = by that much / the more that
• méně = less / fewer
• lidí = of people
• tam = there
• bude = will be

So very literally:

By how much earlier we go to the post office, by that much fewer people there will be.

That is not natural English, but it helps show how the Czech structure works.

Yes, in casual spoken Czech, many people would say míň instead of méně.

So you might hear:

Čím dřív půjdeme na poštu, tím míň lidí tam bude.

That means the same thing. The difference is style:

• méně = more standard / neutral
• míň = more colloquial

Yes, it is completely natural and idiomatic.

A Czech speaker would easily understand it as:

The earlier we go to the post office, the fewer people there will be.

It is a good example of:

• the čím ... tím ... structure
• motion with na + accusative
• a quantity expression: méně lidí
• normal future tense: půjdeme, bude