Mi perdis mian monujon hieraŭ, kaj nun mi ŝuldas monon al mia amiko.

Because monujon is the direct object of perdis (lost), so it takes the accusative ending -n.

In Esperanto, when a noun is the thing directly affected by the verb, it usually gets -n:

• Mi perdis monujon = I lost a wallet.
• Mi perdis mian monujon = I lost my wallet.

The possessive adjective must agree with the noun, so mia also becomes mian:

• mia monujo = my wallet
• mian monujon = my wallet (as a direct object)

Adjectives and related words in Esperanto agree with the noun they describe in number and case.

Since monujon has the accusative -n, mian must also have -n.

Compare:

• mia amiko = my friend
• mian amikon = my friend (as a direct object)

So in the sentence:

• mian monujon = both words show accusative agreement

The ending -is marks the past tense.

So:

• perdi = to lose
• perdas = lose / am losing
• perdis = lost
• perdos = will lose

In this sentence, Mi perdis... hieraŭ means the losing happened in the past, specifically yesterday.

Because the sentence says nun (now), so the owing is true at the present time.

The sentence contrasts two times:

• hieraŭ: I lost my wallet yesterday
• nun: now I owe money to my friend

So:

• Mi perdis mian monujon hieraŭ = a past event
• nun mi ŝuldas monon al mia amiko = a present situation resulting from that event

In Esperanto, mono is also normally an uncountable noun, like money in English.

So:

• mono = money
• monon = money (as a direct object)

Here it is accusative because it is the direct object of ŝuldas:

• mi ŝuldas monon = I owe money

You would only use a plural form like monoj in unusual contexts, such as talking about different currencies or kinds of money.

They are related but different words:

• mono = money
• ujo = container, holder
• monujo = money-holder, wallet/purse

So monujo is built very regularly:

• mon- = money
• -ujo = container for something

A learner will often notice that Esperanto makes many words this way.

Because al means to, and here the friend is the person to whom the money is owed.

So:

• Mi ŝuldas monon al mia amiko = I owe money to my friend

This is a very common use of al for the recipient or target of something.

Compare:

• Mi donis libron al ŝi = I gave a book to her
• Mi skribas al mia frato = I am writing to my brother

Because after a preposition like al, Esperanto normally does not use the accusative -n.

So:

• al mia amiko = to my friend

not

• al mian amikon

The accusative is mainly for direct objects and some expressions of direction/time/measure, but al already shows the relationship clearly.

Yes. Esperanto word order is fairly flexible, as long as the grammar endings make the roles clear.

For example, these are all possible:

• Mi perdis mian monujon hieraŭ, kaj nun mi ŝuldas monon al mia amiko.
• Hieraŭ mi perdis mian monujon, kaj nun mi ŝuldas monon al mia amiko.
• Mi hieraŭ perdis mian monujon, kaj nun mi ŝuldas monon al mia amiko.

Some versions sound more natural than others depending on emphasis, but they are all understandable.

Not always. In Esperanto, commas are often used a bit more by style than by strict necessity, especially before kaj when joining two full clauses.

Here the comma helps separate the two ideas:

• Mi perdis mian monujon hieraŭ
• kaj nun mi ŝuldas monon al mia amiko

So the comma is perfectly fine, but you may also see Esperanto sentences without it in similar cases.

Yes, the present tense already shows that ŝuldas is happening now, but nun adds emphasis and contrast.

Without nun:

• Mi perdis mian monujon hieraŭ, kaj mi ŝuldas monon al mia amiko.

With nun:

• Mi perdis mian monujon hieraŭ, kaj nun mi ŝuldas monon al mia amiko.

The word nun makes the connection clearer: because of what happened yesterday, this is the situation now.

In Esperanto, possessives like mia, via, lia, and so on usually make la unnecessary.

So Esperanto normally says:

• mia amiko = my friend
• mian monujon = my wallet

not usually:

• la mia amiko
• la mian monujon

The possessive already makes the noun definite.

Yes. That is the most natural English equivalent.

Esperanto expresses it as:

• ŝuldi ion al iu = to owe something to someone

So literally:

• Mi ŝuldas monon al mia amiko = I owe money to my friend

But in natural English, I owe my friend money is usually the smoother translation.

Two letters here often stand out to English speakers:

• ŝ is pronounced like sh in ship
• ŭ is a short semivowel, like the w-sound in a diphthong

Examples:

• ŝuldas sounds roughly like SHOOL-dahs
• hieraŭ sounds roughly like hee-EH-rau, with aŭ sounding somewhat like ow in cow

Also remember that Esperanto spelling is very regular: each letter normally has one sound.

It can refer to a wallet or a purse, depending on context.

Literally it just means a container for money. In real usage, speakers may choose the English translation that best fits the situation.

So in this sentence, if you imagine a man’s billfold, wallet is natural; if you imagine a small money-carrying bag or purse, that could also fit.

Esperanto usually uses its simple tense forms where English might choose either a simple tense or a perfect tense.

So:

• Mi perdis mian monujon hieraŭ = I lost my wallet yesterday

Because hieraŭ gives a finished past time, the simple past is exactly what Esperanto wants here.

Esperanto does have compound forms with esti + participle, but they are much less common and are usually used only when a speaker really wants that special nuance.

No. The normal word is simply hieraŭ, without a preposition.

So:

• hieraŭ = yesterday
• hodiaŭ = today
• morgaŭ = tomorrow

Use it directly:

• Mi perdis mian monujon hieraŭ.

not

• en hieraŭ

Here are the main dictionary forms:

• mi = I
• perdi = to lose
• mia = my
• monujo = wallet / purse
• hieraŭ = yesterday
• kaj = and
• nun = now
• ŝuldi = to owe
• mono = money
• al = to
• amiko = friend

Seeing the dictionary forms can help you recognize how endings are working:

• perdis comes from perdi
• ŝuldas comes from ŝuldi
• monon comes from mono
• monujon comes from monujo