Post mallonga paŭzo ni revenas al la klaso kaj aŭskultas bone.

Because mallonga describes the noun paŭzo.

• mallonga = short (adjective)
• mallonge = briefly / in a short way (adverb)

Since paŭzo is a noun, it takes an adjective: mallonga paŭzo = a short break.

If you used mallonge, it would not be modifying paŭzo correctly.

Because mallonga paŭzo is the object of the preposition post, and prepositions normally take the basic form, not the accusative.

So:

• post paŭzo = after a break
• post mallonga paŭzo = after a short break

Also, adjectives match the noun they describe, so if paŭzo has no -n, then mallonga also has no -n.

Post means after.

So:

• post mallonga paŭzo = after a short break

It is a very common preposition for time sequence:

• post la tagmanĝo = after lunch
• post la leciono = after the lesson

Al means to, and reveni al means to return to.

So:

• reveni = to come back / return
• reveni al la klaso = to return to the class / classroom

The preposition al shows the destination.

Compare:

• Ni revenas al la klaso. = We return to the class/classroom.
• Ni estas en la klaso. = We are in the classroom.

So al focuses on movement toward a place.

La is the definite article, meaning the.

In this sentence, la klaso refers to a specific class or classroom that both speaker and listener know about, so Esperanto uses la.

• al klaso would sound more like to a class, which is usually not what is meant here.
• al la klaso = to the class / classroom

Esperanto has only one article, la, and it does not change for gender or number.

It can mean either, depending on context.

Klaso often means:

• class as a group of students
• class as a lesson
• sometimes classroom, especially in simple learning material

In this sentence, English might translate it as either:

• we return to the class
• we return to the classroom

The exact meaning depends on the situation, not on grammar alone.

Because Esperanto often uses the present tense for actions happening now or in a general classroom-style description.

• revenas = return / are returning
• aŭskultas = listen / are listening

This can sound natural in instructions, narration, or descriptions of routine:

• Ni revenas al la klaso kaj aŭskultas bone. = We return to class and listen well.

English sometimes prefers we go back or we come back, but Esperanto uses the simple present here very naturally.

Because the same subject, ni, applies to both verbs.

So this structure means:

• ni revenas ... kaj aŭskultas ...
• literally: we return ... and listen ...

Esperanto often omits repeating the subject when it is clearly the same.

You could say ni revenas al la klaso kaj ni aŭskultas bone, but the second ni is unnecessary unless you want extra emphasis.

Bone is an adverb meaning well.

It modifies the verb aŭskultas:

• aŭskultas bone = listen well

This is the adverb form from bona (good):

• bona = good
• bone = well

So just as English distinguishes good and well, Esperanto distinguishes bona and bone.

Because aŭskulti and aŭdi are different verbs.

• aŭskulti = to listen
• aŭdi = to hear

So:

• Ni aŭskultas bone = We listen well
• Ni aŭdas bone = We hear well

In the sentence, the idea is about paying attention, so aŭskulti is the right verb.

Yes. Esperanto word order is fairly flexible.

These are all possible:

• Ni aŭskultas bone.
• Ni bone aŭskultas.

The first is probably the most neutral and natural here. Putting bone earlier can give it a little more emphasis.

So the sentence uses a normal, straightforward word order, but it is not the only possible one.