Ni devas iri rekte por atingi la bibliotekon antaŭ la vespero.

In Esperanto, modal verbs such as devi (must / have to) are followed directly by an infinitive.

• Ni devas iri = We must go
• Mi volas manĝi = I want to eat
• Ŝi povas veni = She can come

So unlike English, Esperanto does not use a separate word like to before the second verb.

Esperanto verbs do not change according to the subject.

So:

• mi devas = I must
• vi devas = you must
• li devas = he must
• ni devas = we must

The ending -as always marks the present tense. That makes verb conjugation much simpler than in English.

The ending -e marks an adverb in Esperanto.

• rekta = direct, straight
• rekte = directly, straight

In this sentence, rekte describes how we must go:

• iri rekte = go straight / go directly

So the -e ending shows that the word is modifying the verb iri, not acting as an adjective.

Por means for or in order to, and it often introduces a purpose.

So:

• por atingi la bibliotekon = in order to reach the library

This is a very common Esperanto structure:

• Mi lernas por kompreni. = I study in order to understand.
• Li venis por helpi. = He came to help.

So in your sentence, por atingi explains why we must go straight.

Because atingi means to reach, and it takes a direct object.

So:

• atingi la bibliotekon = reach the library

The noun biblioteko gets the -n ending because it is the direct object:

• la biblioteko = the library
• la bibliotekon = the library (as the thing being reached)

You do not need al after atingi, because the verb itself already contains the idea of arriving at or reaching something.

Compare:

• Mi iras al la biblioteko. = I am going to the library.
• Mi atingas la bibliotekon. = I reach the library.

The ending -n marks the direct object in Esperanto.

Here, the thing being reached is the library, so it gets -n:

• atingi la bibliotekon = reach the library

This is one of the most important grammar points in Esperanto. The -n ending often shows what is directly affected by the verb.

Other examples:

• Mi vidas la domon. = I see the house.
• Ŝi legas la libron. = She reads the book.

In your sentence, la bibliotekon is what we are trying to reach.

La is the definite article in Esperanto, meaning the.

So:

• biblioteko = a library / library
• la biblioteko = the library

In this sentence, it refers to a specific library that the speakers already have in mind, so la is used.

A nice thing about Esperanto is that la never changes:

• no different forms for gender
• no different forms for case
• no plural change

Even when the noun takes -n, the article stays the same:

• la biblioteko
• la bibliotekon

Antaŭ means before in a time sense, and also in front of in a location sense. Here it clearly means before because it refers to time.

• antaŭ la vespero = before the evening

So the sentence means that the library must be reached before evening comes.

Context tells you whether antaŭ is about time or place:

• antaŭ la domo = in front of the house
• antaŭ la vespero = before the evening

Both can be possible in Esperanto depending on style and context, but la vespero often means the evening in a general, understood sense.

So:

• antaŭ vespero can feel more like before evening / by evening
• antaŭ la vespero can feel a little more definite: before the evening

Esperanto often uses la with parts of the day when they are treated as a specific time period.

Esperanto word order is fairly flexible, but this sentence uses a very natural and clear order:

• Ni devas iri rekte = main statement
• por atingi la bibliotekon = purpose
• antaŭ la vespero = time limit

Because Esperanto marks grammar clearly with endings, some rearrangement is possible. For example, you could say:

• Por atingi la bibliotekon antaŭ la vespero, ni devas iri rekte.

That means essentially the same thing. The original order just sounds straightforward and neutral.

Yes. It can suggest either:

• go straight
• go directly

The exact nuance depends on context.

If people are talking about directions on a route, iri rekte often means go straight ahead.

If they are talking more generally about the plan, it can mean go directly, without detours.

So this phrase is natural in both a physical and practical sense.

Because atingi focuses on reaching a destination, while arrive in Esperanto is usually expressed differently, for example with alveni.

Compare:

• Ni devas atingi la bibliotekon. = We must reach the library.
• Ni devas alveni al la biblioteko. = We must arrive at the library.

Both can work, but they are built differently:

• atingi takes a direct object: la bibliotekon
• alveni normally uses al: al la biblioteko

So the sentence is using a perfectly normal way to express the idea of reaching the destination.

A helpful breakdown is:

• Ni = we
• devas = must / have to
• iri = go
• rekte = straight / directly
• por = in order to
• atingi = reach
• la bibliotekon = the library
• antaŭ la vespero = before the evening

So the structure is:

subject + modal verb + infinitive + adverb + purpose phrase + time phrase

That pattern is very common and useful in Esperanto.