Vom Bahnhof bis zur Bibliothek ist es nur ein Kilometer.

Vom is a contraction of von dem.

• von = from
• dem = the (dative masculine/neuter)

So:

• vom Bahnhof = from the train station

German uses this contraction very often, and von dem would usually sound less natural here.

Because the nouns have different grammatical genders, and von and zu both require the dative case.

• der Bahnhof is masculine

  • dative: dem Bahnhof
  • von dem → vom Bahnhof

• die Bibliothek is feminine

  • dative: der Bibliothek
  • zu der → zur Bibliothek

So the gender of the noun changes the article:

• masculine/neuter dative: dem
• feminine dative: der

With places, German often uses bis zu when referring to a destination or endpoint, especially with a noun phrase that has an article.

So:

• bis zur Bibliothek = as far as the library / up to the library

Using only bis is more common before:

• adverbs: bis dort
• city names or some place names without articles: bis Berlin
• time expressions: bis morgen

When there is a noun with an article, bis zu is very common and natural.

It gives the distance span: from the station to the library.

It works like a prepositional phrase describing the two points between which the distance is measured.

So the sentence structure is roughly:

• Vom Bahnhof bis zur Bibliothek = from the station to the library
• ist es = it is
• nur ein Kilometer = only one kilometer

English often says It is only one kilometer from the station to the library, but German can naturally start with the distance span instead.

Because German main clauses follow the verb-second rule.

The first position in a sentence can be filled by many kinds of elements, not just the subject. Here, the whole phrase:

• Vom Bahnhof bis zur Bibliothek

comes first.

That means the finite verb must come next:

• Vom Bahnhof bis zur Bibliothek ist ...

Then the subject-like element es comes after the verb.

This is completely normal German word order.

This es is a kind of dummy subject or formal subject, similar to English it in sentences like:

• It is far
• It is one kilometer

German often uses es in distance, weather, time, and general-condition expressions.

Here, es does not refer to a specific thing. It is just needed to complete the sentence structure:

• ... ist es nur ein Kilometer.

Because ein Kilometer is not a direct object here. It is part of the predicate after sein.

The verb sein does not take an accusative object the way many action verbs do. Instead, it links the subject structure to a description or identification.

So:

• Es ist ein Kilometer.

is like:

• It is one kilometer.

That is why ein Kilometer stays in the nominative form.

Because Kilometer is a masculine noun:

• der Kilometer

So in the nominative singular:

• ein Kilometer

If it were a feminine noun, it would be eine.

Both are possible, but they are slightly different structures.

• Es ist nur ein Kilometer.
  This is a very common, simple way to express distance.

• Es ist nur einen Kilometer weit.
  This is also correct, but here weit is included, and einen Kilometer functions differently.

The version in your sentence is very natural and common in everyday German.

Yes. That is another natural way to express the same idea.

A few common alternatives are:

• Vom Bahnhof bis zur Bibliothek ist es nur ein Kilometer.
• Die Bibliothek ist nur einen Kilometer vom Bahnhof entfernt.
• Der Bahnhof ist nur einen Kilometer von der Bibliothek entfernt.

They all express the same basic meaning, but the focus shifts slightly depending on what comes first.

Usually yes.

• der Bahnhof normally means train station or railway station

If you want to talk about a bus stop, that would usually be:

• die Bushaltestelle

So learners should be careful not to translate Bahnhof as just any kind of station or stop.

Because in German, all nouns are capitalized.

So in this sentence:

• Bahnhof
• Bibliothek
• Kilometer

all begin with capital letters.

This is one of the most noticeable spelling rules in German.

A very literal version would be:

• From the station to the library it is only one kilometer.

That sounds a bit marked in English, but it helps show the German structure.

A more natural English version is usually:

• It’s only one kilometer from the station to the library.

So the meaning is the same, but German and English prefer different sentence orders in neutral style.