Ni portas kartonon kaj reuzpaperon al la deponejo.

Because they are the direct objects of portas.

In Esperanto, the thing that receives the action usually takes the accusative ending -n. Here, what are we carrying?

• kartonon
• reuzpaperon

So both nouns get -n.

Base forms:

• kartono = cardboard / carton material
• reuzpapero = reusable or recycling paper, depending on context

In the sentence, they become:

• kartonon
• reuzpaperon

Because la deponejo is not the direct object here. It is part of the prepositional phrase al la deponejo, meaning to the depot / to the drop-off place.

The preposition al already shows direction, so deponejo does not need an accusative ending here.

So:

• kartonon = object being carried
• al la deponejo = destination

A useful rule: if a noun is governed by a preposition like al, it usually does not take -n just for that reason.

Al means to. It shows the destination or recipient.

So al la deponejo means to the depot or to the collection point.

It answers the question where to?

Compare:

• Mi donas ĝin al ŝi. = I give it to her.
• Ni iras al la urbo. = We are going to the city.

In your sentence, al shows where the cardboard and paper are being taken.

Porti basically means to carry, to take, or sometimes to wear, depending on context.

Here, because the sentence has objects and a destination, portas means something like:

• carry
• take
• bring

So Ni portas ... al la deponejo can be understood as We are taking/carrying ... to the depot.

Also note:

• portas is present tense
• Ni portas = we carry / we are carrying / we take, depending on context

Esperanto present tense often covers both simple present and present continuous, just like many Esperanto verbs do in translation.

Because Esperanto very often forms new meanings by making compound words.

Here:

• reuz- = reuse
• papero = paper

Together:

• reuzpapero = reuse-paper, meaning a kind of paper associated with reuse or recycling

Writing compounds as one word is extremely normal in Esperanto. It is one of the language’s most productive patterns.

An English speaker may expect two words, but Esperanto often prefers a compact compound when the two parts form one clear idea.

Possibly, but it would not mean exactly the same thing.

• reuzpapero is a compound noun: it names a type/category of paper.
• reuza papero means reusable paper more literally, with reuza acting as an adjective.

So the difference is roughly:

• reuzpapero = reuse/recycling paper as a category
• reuza papero = paper that is reusable

Esperanto often uses a compound when a speaker thinks of something as a single category rather than just a noun with a descriptive adjective.

Yes. -ej- is a very common Esperanto suffix meaning place for or place where something happens.

So:

• deponi = to deposit, to place, to put into storage
• depon- = the root
• -ej- = place
• -o = noun ending

That gives:

• deponejo = a deposit-place, storage place, depot, drop-off point

This is a very typical Esperanto word-building pattern. For example:

• lerni = to learn → lernejo = school
• kuiri = to cook → kuirejo = kitchen
• vendi = to sell → vendejo = shop/store

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

So:

• la deponejo = the depot
• deponejo = a depot or just depot, depending on context

In your sentence, la deponejo suggests a specific depot or collection place that the speaker and listener can identify.

This is normal Esperanto usage:

• Mi vidas la domon. = I see the house.
• Mi vidas domon. = I see a house.

Because these words can function like mass nouns or category nouns, just as in English.

In this sentence, the speaker is probably talking about the material:

• cardboard
• paper for reuse/recycling

So singular is natural:

• kartono
• reuzpapero

Esperanto often uses the singular for materials or substances unless the speaker wants to emphasize separate individual items.

If you were talking about distinct objects, plurals might be possible, but here the singular sounds very natural.

No. Esperanto word order is fairly flexible, because endings and prepositions make the grammar clear.

This sentence is the most neutral order:

• subject → verb → object → destination

But other orders are possible for emphasis, for example:

• Al la deponejo ni portas kartonon kaj reuzpaperon.
• Kartonon kaj reuzpaperon ni portas al la deponejo.

These mean essentially the same thing, but the emphasis changes slightly. The original version is the most straightforward and easiest for learners.

In standard Esperanto, each direct object noun normally takes its own accusative ending.

So:

• kartonon kaj reuzpaperon

not:

• kartono kaj reuzpaperon

Since both nouns are direct objects of portas, both should be marked. This is especially helpful because Esperanto likes clear, regular marking.