Li pagis la monpunon hieraŭ.

Because -is is the Esperanto past-tense ending for verbs.

• pagi = to pay
• pagas = pays / is paying
• pagis = paid
• pagos = will pay

So Li pagis la monpunon hieraŭ means that the paying happened in the past.

Li means he.

In Esperanto, you normally include the subject pronoun unless the subject is clear from context in some special situation. So:

• Li pagis = He paid

Unlike English, Esperanto verb forms do not change according to person, so pagis by itself does not tell you whether the subject is I, you, he, she, they, etc. That is why li is important here.

The -n ending marks the direct object.

In this sentence, the fine is the thing that was paid, so it is the direct object:

• Li pagis la monpunon = He paid the fine

The base noun is:

• monpuno = a fine, a monetary penalty

After la, it becomes la monpuno = the fine

And because it is the direct object, it becomes:

• la monpunon

This -n is called the accusative ending.

La is the Esperanto definite article, meaning the.

So:

• monpuno = a fine
• la monpuno = the fine

In your sentence, la monpunon means the fine. The article does not change for gender, number, or case; the -n goes on the noun, not on la.

Monpuno means fine in the sense of a money penalty.

It is built from:

• mono = money
• puno = punishment / penalty

So monpuno literally means something like money-penalty.

This helps show how Esperanto often builds words from smaller meaningful parts.

Yes, it could go somewhere else. Hieraŭ means yesterday, and Esperanto word order is fairly flexible.

All of these are possible:

• Li pagis la monpunon hieraŭ.
• Hieraŭ li pagis la monpunon.
• Li hieraŭ pagis la monpunon.

The most neutral version here is probably the original one. Moving hieraŭ can change the emphasis a little, but not the basic meaning.

No, it is usually more flexible than English because endings show grammatical roles.

In English, word order is very important:

• He paid the fine ≠ The fine paid he

In Esperanto, the -n on the direct object helps make the meaning clear. So you can change the order more freely, for example:

• Li pagis la monpunon.
• La monpunon li pagis.

Both can mean He paid the fine, though the second one gives special emphasis to the fine.

Yes. Esperanto past tense does not make a basic distinction like English sometimes does between simple past and emphatic did.

So Li pagis la monpunon can match:

• He paid the fine
• He did pay the fine

If you want special emphasis, you usually show that through context, stress, or extra words.

A helpful breakdown is:

• hi-e-raŭ

Esperanto pronunciation is regular, and each vowel is pronounced clearly. The ŭ here is a very short w-like sound, so aŭ sounds a bit like the ow in cow.

Also, the stress in Esperanto normally falls on the second-to-last syllable, so:

• hi-e-RAŬ

In Esperanto, each word is stressed on the next-to-last syllable.

So:

• Li → only one syllable
• PAgis
• monPUnon
• hi-eRAŬ

That regular stress pattern is one thing many learners find helpful.

Esperanto has la for the, but it does not have an indefinite article like English a/an.

So:

• monpuno can mean a fine or just fine depending on context
• la monpuno means the fine

In your sentence, la makes it definite: the fine.

Not exactly as written. Because of la, it specifically means the fine.

If you wanted He paid a fine yesterday, you would usually say:

• Li pagis monpunon hieraŭ.

Without la, the noun is indefinite.

No. Hieraŭ simply gives a time reference: yesterday.

The verb form pagis is already past tense, so the sentence is fully grammatical and natural:

• Li pagis la monpunon hieraŭ.

Esperanto does not require a special perfect form here. If needed, Esperanto can form more complex tenses, but the simple past is very commonly used.

Yes. The plural of monpuno is monpunoj.

If it were the direct object in plural, you would use both -j and -n:

• Li pagis la monpunojn. = He paid the fines.

So the order of endings is:

• noun root + -o
• plural -j if needed
• accusative -n if needed

That gives monpuno, monpunoj, or monpunojn.

Yes. Only the pronoun changes:

• Li = he
• Ŝi = she

Everything else works exactly the same:

• Ŝi pagis la monpunon hieraŭ. = She paid the fine yesterday.

That is another useful thing about Esperanto: verbs do not change depending on the subject.