La asocio sendis mesaĝon al la retbutiko.

The ending -is marks the past tense in Esperanto. So sendis means sent.

A useful pattern is:

• sendas = sends / is sending
• sendis = sent
• sendos = will send
• sendus = would send
• sendi = to send

So La asocio sendis... means the association did the sending in the past.

In Esperanto, verbs do not change according to person or number. The same verb form is used with I, you, he, she, it, we, and they.

So:

• mi sendis = I sent
• li sendis = he sent
• la asocio sendis = the association sent
• ili sendis = they sent

This is much simpler than English, because you do not have to learn separate forms like send and sends.

The -n ending marks the direct object in Esperanto.

Here, the message is the thing being sent, so it is the direct object:

• La asocio = the association → the subject
• sendis = sent → the verb
• mesaĝon = a message / the message → the direct object

So mesaĝon has -n because it receives the action of the verb.

Because la retbutiko is not the direct object here. It is the recipient, introduced by the preposition al.

• mesaĝon = what was sent
• al la retbutiko = to the online shop

Normally, after a preposition like al, the noun does not take the accusative -n. The preposition already shows its role.

So:

• sendis mesaĝon = sent a message
• al la retbutiko = to the online shop

Al usually means to and often shows the destination or recipient of something.

In this sentence, it marks who received the message:

• La asocio sendis mesaĝon al la retbutiko.
• The association sent a message to the online shop.

You will often see al with verbs of giving, sending, saying, writing, and showing.

For example:

• Mi donis la libron al ŝi. = I gave the book to her.
• Li skribis al mi. = He wrote to me.

Esperanto has only one article: la, which means the. There is no separate word for a/an.

So in this sentence:

• la asocio = the association
• la retbutiko = the online shop
• mesaĝon = a message / message

The lack of la before mesaĝon usually makes it sound indefinite, like English a message, rather than the message.

So this sentence naturally suggests:

• a specific association
• a specific online shop
• an unspecified message

Yes, it is a normal Esperanto compound word.

It is made from:

• ret- = net / internet / online
• butiko = shop

So retbutiko literally means internet-shop, or more naturally, online shop.

A helpful rule in Esperanto is that the main idea usually comes last. So a retbutiko is a kind of butiko.

Compare:

• librobutiko = bookshop
• retpaĝo = webpage
• retadreso = internet address / web address

Esperanto makes this very clear through grammar.

In this sentence:

• La asocio has no -n, so it is the subject
• mesaĝon has -n, so it is the direct object
• al la retbutiko is a prepositional phrase showing the recipient

So even if you are not relying on word order, the grammar tells you the roles.

That is one of the big advantages of Esperanto: sentence structure is often clearer because endings do a lot of the work.

Yes, Esperanto word order is fairly flexible, because endings and prepositions show the grammatical roles.

The most neutral order here is:

• La asocio sendis mesaĝon al la retbutiko.

But other orders are possible, for example:

• Mesaĝon la asocio sendis al la retbutiko.
• Al la retbutiko la asocio sendis mesaĝon.

These still mean basically the same thing, but the emphasis changes a little. The original order is the most straightforward and natural for a beginner to use.

In Esperanto, stress normally falls on the second-to-last syllable of each word.

So the stress is:

• LA
• a-so-CI-o
• SEN-dis
• me-SA-ĝon
• AL
• LA
• ret-bu-TI-ko

A few pronunciation notes:

• c in asocio sounds like ts
• ĝ in mesaĝon sounds like the j in jam
• j and ĝ are different letters in Esperanto

So asocio sounds roughly like a-so-TSI-o, and mesaĝo like me-SA-jo with a strong English-style j sound.