Se la libro estas utila, mi aĉetos ĝin tie mem en la librovendejo.

Se means if. It introduces a condition:

• Se la libro estas utila = If the book is useful
• mi aĉetos ĝin = I will buy it

So the whole sentence has a clear condition + result structure.

Because the sentence is talking about a present condition and a future result.

• estas = is / are (present tense)
• aĉetos = will buy (future tense)

So the idea is:

• if the book is useful,
• then I will buy it.

This is very natural in Esperanto. The usefulness is being judged now, while the buying happens afterward.

The ending -os marks the future tense in Esperanto.

So:

• aĉeti = to buy
• aĉetas = buys / is buying
• aĉetos = will buy
• aĉetis = bought

Esperanto uses verb endings instead of a separate word like will.

Because utila is an adjective, and Esperanto adjectives end in -a.

• utilo = usefulness, utility
• utila = useful

Here it describes la libro, so la libro estas utila means the book is useful.

Also, because utila is after estas, it is a predicate adjective, so it does not take -n here.

Because ĝin is the direct object form.

• ĝi = it
• ĝin = it as a direct object

In the sentence, the book is the thing being bought, so it is the object of aĉetos:

• mi aĉetos ĝin = I will buy it

The final -n marks the accusative, which is often used for direct objects in Esperanto.

Because ĝi can refer to a thing, and a book is a thing.

So once la libro has already been mentioned, Esperanto can replace it with ĝin to avoid repetition:

• Se la libro estas utila, mi aĉetos la libron would be possible but repetitive
• Se la libro estas utila, mi aĉetos ĝin sounds more natural

Tie means there, and mem adds emphasis.

So tie mem means something like:

• right there
• there itself
• on the spot

In this sentence, it strengthens the idea that the speaker will buy the book right there, not somewhere else or later.

Important: mem is an emphasizing word. It does not mean myself here.

They are closely related, but not identical.

• tie mem emphasizes the location: right there
• en la librovendejo names the place: in the bookstore

Together they create a stronger expression, like:

• right there in the bookstore
• on the spot, in the bookstore itself

So this is not wrong or unusual; it is just more emphatic than using only one of them.

It is a compound word made from several parts:

• libro = book
• vend- = sell
• -ej- = place
• -o = noun ending

So:

• librovendejo = a place for selling books = bookstore / bookshop

This is a very typical Esperanto word-building pattern.

La is Esperanto’s definite article, meaning the.

So:

• la libro = the book
• la librovendejo = the bookstore

Esperanto has only one article, la, and it does not change for gender, number, or case.

There is no separate word for a/an in normal Esperanto.

Yes, Esperanto word order is fairly flexible, though some orders sound more natural than others.

The given order is very natural:

• Se la libro estas utila, mi aĉetos ĝin tie mem en la librovendejo.

But you could also say:

• Mi aĉetos ĝin tie mem en la librovendejo, se la libro estas utila.

That still means the same thing.

Because Esperanto marks grammar clearly with endings like -n, it often allows more freedom in word order than English does.

In this sentence:

• ĉ in aĉetos sounds like ch in church
• ĝ in ĝin sounds like j in judge

So approximately:

• aĉetos ≈ ah-CHEH-toss
• ĝin ≈ jeen with the j sound from judge

These accented letters are separate letters in the Esperanto alphabet, not just decorative variations.

Because Se la libro estas utila is a subordinate if-clause, and it is followed by the main clause.

So the comma helps separate:

• the condition
• the result

This is standard and makes the sentence easier to read.