La kuriero atendas apud la pordo.

Because each noun phrase gets its own article. La means the, and Esperanto uses it before a noun when that noun is definite.

So:

• la kuriero = the courier
• la pordo = the door

You do not usually use one la to cover both nouns across the sentence.

In Esperanto, nouns normally end in -o. So kuriero is a noun meaning courier.

This is one of the most basic and helpful patterns in Esperanto:

• -o = noun
• -a = adjective
• -e = adverb
• -i = dictionary form of a verb
• -as = present tense verb

Because of this, a learner can immediately recognize kuriero as a noun.

No. By default, Esperanto nouns like kuriero are not specifically masculine. It simply means courier.

If you want to make the person explicitly female, Esperanto often uses -in-:

• kuriero = courier
• kurierino = female courier

But in ordinary usage, kuriero can refer to a person of any gender unless the context says otherwise.

Because -as marks the present tense.

• atendi = to wait
• atendas = waits / is waiting

So La kuriero atendas means The courier waits or The courier is waiting.

In Esperanto, the present tense often covers both the simple present and the English present progressive.

It can do both, depending on context.

• La kuriero atendas. = The courier is waiting.
• La kuriero atendas la pakon. = The courier is waiting for the package / expecting the package.

So atendi can be used without an object, as in your sentence, or with a direct object.

Apud means beside, next to, or by in the sense of being nearby.

So apud la pordo means the courier is positioned near the door, right by it or beside it.

It is a more specific location word than a very general at.

Yes, often you could, but the nuance is a little different.

• apud la pordo = beside the door, next to it
• ĉe la pordo = at the door, by the door

Ĉe is broader and more general. Apud emphasizes physical closeness alongside something. In many situations both are acceptable, but apud paints a slightly more precise picture.

Because la pordo is the object of the preposition apud, and in this sentence there is no reason to add -n.

The -n ending is mainly used for:

• direct objects
• direction in some expressions

Here, apud la pordo is just a location phrase: the courier is waiting beside the door. It is not a direct object.

So:

• correct here: apud la pordo
• not needed here: apud la pordon

Because kuriero is the subject of the sentence, not the direct object.

In La kuriero atendas apud la pordo:

• la kuriero = the one doing the action
• atendas = the action
• apud la pordo = where the action happens

Subjects normally do not take -n.

Not completely. The normal, straightforward order is:

La kuriero atendas apud la pordo.

But Esperanto allows some flexibility, especially with phrases like apud la pordo:

• Apud la pordo la kuriero atendas.
• Apud la pordo atendas la kuriero.

These are still understandable, though the original version is the most neutral and natural for a beginner.

Esperanto pronunciation is very regular. Stress falls on the second-to-last syllable.

Approximate pronunciation:

• la → lah
• kuriero → koo-ree-EH-ro
• atendas → ah-TEN-das
• apud → AH-pood
• pordo → POR-do

A few useful points:

• r is usually tapped or rolled
• each vowel is pronounced clearly
• the stress rule is very consistent

Esperanto has a definite article, la = the, but it does not have an indefinite article like a or an.

So:

• kuriero can mean a courier or just courier, depending on context
• la kuriero means the courier

That is why learners often notice that Esperanto uses la, but nothing equivalent to English a/an.

Yes. The Esperanto present tense -as can match both of those English forms.

So La kuriero atendas apud la pordo can be translated naturally as:

• The courier waits by the door.
• The courier is waiting by the door.

English chooses between simple present and progressive more often than Esperanto does.