Ni alŝutas datumojn al la retejo.

Because it has two endings attached:

• -j = plural
• -n = accusative, which usually marks the direct object

So:

• datumo = one datum / one piece of data
• datumoj = data, plural
• datumojn = data, plural, as the direct object

In this sentence, datumojn is the thing being uploaded, so it takes -n.

The dictionary form is datumo.

Esperanto words are usually learned in their basic form:

• nouns end in -o
• adjectives end in -a
• verbs are usually listed in the infinitive -i

So datumojn breaks down like this:

• datum- = the root
• -o = noun
• -j = plural
• -n = accusative

A learner should recognize that the core noun here is datumo.

Because Esperanto does not have an indefinite article like English a/an.

It only has the definite article la = the.

So Esperanto can say simply datumojn without any article. Depending on context, that can mean things like:

• data
• some data
• the data

In this sentence, the meaning is understood from context, so no article is needed.

Al is a preposition meaning to.

It shows the direction or destination of the uploading. The data is being uploaded to the website, so Esperanto uses al la retejo.

This is very normal:

• iri al la urbo = go to the city
• sendi ion al iu = send something to someone
• alŝuti datumojn al la retejo = upload data to the website

Because it is not the direct object.

The direct object is datumojn. That is the thing being uploaded.

La retejo is part of a prepositional phrase introduced by al, so al already shows its role. Normally, nouns after prepositions do not take -n just for that reason.

So:

• datumojn = direct object → gets -n
• al la retejo = prepositional phrase → no accusative needed here

It is a normal Esperanto compound verb:

• al- = a prefix meaning to, toward, onto, adding to
• ŝut- = the root
• -as = present tense verb ending

So alŝutas is a single verb meaning uploads.

Esperanto often builds words this way instead of using completely separate unrelated words. That is one of the language’s most important features: word-building is very regular.

A learner should get used to seeing verbs made from:

• a prefix
• a root
• a grammatical ending

-as is the present tense ending.

So alŝutas means the action is in the present. Depending on context, that can correspond to English:

• upload
• uploads
• are uploading
• is uploading

Esperanto present tense is often broader than English. It does not force the same distinction English makes between we upload and we are uploading. Context decides that.

Retejo is also built very regularly:

• ret- = net / network
• -ej- = place
• -o = noun

So retejo literally means something like a place on the net. In normal use, it means website.

This is a great example of Esperanto word-building. The middle element -ej- often means place for or place connected with:

• lernejo = school
• kuirejo = kitchen
• retejo = website

Not completely, but the given order is the most neutral and natural one.

This sentence uses a standard pattern:

• Ni = subject
• alŝutas = verb
• datumojn = direct object
• al la retejo = prepositional phrase

Because Esperanto marks the direct object with -n, word order is more flexible than in English. But learners should usually start with the normal order used here.

For example, Ni alŝutas datumojn al la retejo is the safest, most natural version for ordinary use.

In Esperanto, the verb ending shows tense, but not person.

So alŝutas tells you the action is in the present, but it does not by itself mean we upload. It could be:

• I upload
• you upload
• we upload
• they upload
• etc.

That is why the subject pronoun ni is needed. Ni specifically means we.

A rough guide:

• alŝutas ≈ ahl-SHOO-tahs
• datumojn ≈ dah-TOO-moyn
• retejo ≈ reh-TEY-yoh

A few important pronunciation points:

• ŝ sounds like English sh
• j sounds like English y
• oj sounds roughly like oy
• stress in Esperanto normally falls on the second-to-last syllable

So:

• al-ŜU-tas
• da-TU-mojn
• re-TE-jo

That regular pronunciation system is one of Esperanto’s easiest features once you learn the letters.