La komercisto montras tekruĉon al la aĉetanto.

The -n is the accusative ending. In Esperanto, it usually marks the direct object of the verb — the thing directly affected by the action.

Here, montras means shows, so the thing being shown is tekruĉon.

• tekruĉo = a teapot
• tekruĉon = a teapot, as the direct object

So:

• La komercisto montras tekruĉon = The merchant shows a teapot

Without the -n, the noun would just be in its basic form and would not be marked as the direct object.

Because al means to, and it marks the recipient or target of the action.

In English, we say:

• shows a teapot to the buyer

In Esperanto, that to the buyer part is:

• al la aĉetanto

So the sentence is structured like this:

• La komercisto = the merchant
• montras = shows
• tekruĉon = a teapot
• al la aĉetanto = to the buyer

You usually do not add -n after al, because the preposition already shows the role of the noun.

Al usually means to, toward, or for, depending on context. Here it clearly means to.

So:

• al la aĉetanto = to the buyer

It shows who receives the action of showing.

Compare:

• Mi donas libron al ŝi. = I give a book to her.
• Li skribas al la amiko. = He writes to the friend.

In your sentence, the merchant is showing something to someone, so al is the natural choice.

Montras is the verb montri in the present tense.

Esperanto verb endings are very regular:

• -as = present
• -is = past
• -os = future
• -us = conditional
• -u = command/wish
• -i = infinitive

So:

• montri = to show
• montras = shows / is showing

Also, Esperanto verbs do not change according to the subject:

• mi montras = I show
• vi montras = you show
• li montras = he shows
• la komercisto montras = the merchant shows

The ending stays -as for all persons.

Because both nouns are being treated as specific:

• la komercisto = the merchant
• la aĉetanto = the buyer

Esperanto uses la as its definite article, like English the. It does not change for gender, number, or case.

So all of these use the same la:

• la viro = the man
• la virino = the woman
• la libroj = the books
• la libron = the book (as object)

In your sentence, both the merchant and the buyer are understood as definite, so both get la.

Komercisto is made from:

• komerc- = trade, commerce
• -ist- = a person professionally or habitually involved in something
• -o = noun ending

So:

• komercisto = merchant, trader

The suffix -ist- is very common in Esperanto:

• pianisto = pianist
• artisto = artist
• dentisto = dentist

So a learner can recognize komercisto as someone whose role or profession is connected with trade.

Aĉetanto comes from:

• aĉet- = buy
• -ant- = present active participle, meaning someone doing the action
• -o = noun ending

So literally it means:

• aĉetanto = someone who is buying = buyer

This is a very common Esperanto pattern:

• parolanto = speaker
• lernanto = learner/student
• laboranto = worker

So la aĉetanto is the buyer.

Yes, it is a compound word.

It is built from:

• te- = tea
• kruĉo = jug, pot, pitcher
• -n = accusative ending

So:

• tekruĉo = teapot
• tekruĉon = teapot, as the direct object

In Esperanto compounds, the first part often appears without its final noun ending:

• teo
  • kruĉo → tekruĉo

This is very normal in Esperanto word-building.

Yes, to some extent.

Because Esperanto marks roles with endings and prepositions, the word order is more flexible than in English.

The neutral order here is:

• La komercisto montras tekruĉon al la aĉetanto.

But you could also say things like:

• Tekruĉon la komercisto montras al la aĉetanto.
• Al la aĉetanto la komercisto montras tekruĉon.

These are grammatical because:

• tekruĉon has -n, so we know it is the direct object
• al la aĉetanto is marked by al, so we know it means to the buyer

That said, the original order is the most straightforward and natural for most situations.

It can mean either, depending on context.

Esperanto -as simply marks the present tense. It does not force the distinction that English sometimes makes between:

• shows
• is showing

So:

• La komercisto montras tekruĉon al la aĉetanto.

could mean:

• The merchant shows a teapot to the buyer
• The merchant is showing a teapot to the buyer

Usually the context tells you which is more natural.

Yes. In standard Esperanto, nouns end in -o.

Examples from this sentence:

• komercisto
• tekruĉo
• aĉetanto

If you make them plural, you add -j:

• komercistoj = merchants
• tekruĉoj = teapots
• aĉetantoj = buyers

If they are also direct objects, you add -n after that:

• tekruĉojn = teapots, as direct objects

This regularity is one of the main features of Esperanto grammar.

Because Esperanto usually uses prepositions for meanings like to, from, with, for, and so on.

Here, al already tells us the relationship:

• al la aĉetanto = to the buyer

So no extra case ending is needed.

Esperanto mainly uses -n for:

1. direct objects
2. movement toward something in some expressions

Since la aĉetanto is not the direct object here, and since al already marks the role, the plain form aĉetanto is used.