Što je vrh bliže, to idemo brže.

This is a very common Serbian pattern that matches English the ..., the ... in sentences like:

The closer the summit is, the faster we go.

So:

• što je vrh bliže = the closer the summit is
• to idemo brže = the faster we go

Here, što does not mean what. It is part of a fixed comparative-correlative structure: što X, to Y.

A similar example is:

Što više učiš, to više znaš.
The more you study, the more you know.

In a basic sentence, yes, you would normally say:

Vrh je bliže.
The summit is closer.

But je is a clitic in Serbian. Clitics usually go in the second position in their clause.

In this sentence, the clause begins with što, so the clitic je comes right after it:

Što je vrh bliže ...

So this word order is not random; it follows the normal Serbian clitic-placement rule.

Vrh is in the nominative singular.

It is the subject of the clause:

vrh je bliže = the summit is closer

Many masculine nouns in Serbian have no ending in the nominative singular, so vrh is already the dictionary form.

This is a very natural question, because English speakers often expect an adjective here.

In Serbian, for physical distance, speakers very often use blizu / bliže in a predicative way:

• Kuća je blizu. = The house is near.
• Stanica je bliže. = The station is closer.
• Vrh je bliže. = The summit is closer.

So bliže is the normal form here.

By contrast, bliži is the adjective form that agrees with a noun in gender/number/case, for example:

• bliži vrh = the nearer summit
• bliži rođak = a closer relative

So in this sentence, bliže is the expected choice.

Because brže modifies the verb idemo.

• brz = fast as an adjective
• brzo = fast / quickly as an adverb
• brže = faster / more quickly (comparative adverb)

So:

idemo brže = we go faster

If you used the adjective, it would describe a noun or a subject, for example:

• Mi smo brži. = We are faster.

But here the sentence is about how we go, so the adverb brže is correct.

Because Serbian often leaves subject pronouns out when they are already clear from the verb form.

Idemo already means we go / we are going because the ending -mo shows first person plural.

So:

• idem = I go
• ideš = you go
• ide = he/she/it goes
• idemo = we go

You can add mi if you want emphasis or contrast:

Mi idemo brže, a oni sporije.
We go faster, and they go more slowly.

But in your sentence, mi is unnecessary.

Because Serbian does not have articles like the and a/an.

So vrh can mean:

• a summit
• the summit
• sometimes just summit/top

Which one is meant depends on context.

That is completely normal in Serbian.

In this construction, you should use što.

Although šta is very common in everyday speech as a form of what, the pattern here is a fixed grammatical one:

što ..., to ...

So the standard and natural form is:

Što je vrh bliže, to idemo brže.

Yes, Serbian word order is fairly flexible.

So both of these are possible:

• to idemo brže
• to brže idemo

The version with brže earlier can sound a bit more emphatic. The original sentence is natural and neutral.

A quick guide:

• š = sh in ship
• ž = the sound in measure or vision

So:

• što sounds roughly like shto
• bliže sounds roughly like BLEE-zheh

The hardest word is vrh. It is basically one syllable, and the r acts like the center of the syllable. English does not really have this exact sound pattern.

A rough approximation is something like vrh said quickly, with:

• a short v
• an r sound that carries the syllable
• a clear final h

And:

• brže is roughly BR-zheh, with that same kind of syllabic r

This is one of those sounds that becomes much easier with listening and repetition than with English-style spelling.