Learn Hardcore Esperanto: Antaŭ la naskiĝtago de mia fratino mi serĉas ideojn en la interreto kaj legas unu retejon pri donacoj. - Before my sister's birthday I look for ideas on the internet and read one website about presents.

habitual actions
- Antaŭ la naskiĝtago de mia fratino mi serĉas ideojn…
  = Before my sister’s birthday I (usually) look for ideas…
planned / scheduled actions, if the time expression already makes it clear

If you want to talk about one specific future occasion, you can use the future tense:

Antaŭ la naskiĝtago de mia fratino mi serĉos ideojn en la interreto kaj legos unu retejon pri donacoj.
= Before my sister’s birthday I will look for ideas on the internet and will read one website about gifts.

So the given sentence with present tense is most naturally understood as a repeated or typical behavior, not a one-time future event.

Why does naskiĝtago not have -n after antaŭ? Should it be antaŭ la naskiĝtagon?

Prepositions in Esperanto (like antaŭ) normally take nouns without -n:

antaŭ la domo = in front of the house
antaŭ la vespero = before the evening

So antaŭ la naskiĝtago de mia fratino is perfectly standard: before my sister’s birthday.

You sometimes see -n with prepositions to show direction or movement (especially in space or time), but that is optional and more advanced usage. For a simple “before X” in time, you normally just say:

antaŭ la naskiĝtago (no -n)

Why do we say la naskiĝtago de mia fratino and not use a possessive like mia fratino naskiĝtago?

Esperanto usually shows possession in two main ways:

With de
- owner:
  - la naskiĝtago de mia fratino = the birthday of my sister
With a possessive adjective directly before the noun:
- mia fratino = my sister
- mia frato = my brother

But you normally don’t use the possessive directly in front of another noun like in English “my sister’s birthday”.
Structures like mia fratina naskiĝtago would be grammatically possible but feel artificial or unclear.

So the natural way is:

la naskiĝtago de mia fratino = my sister’s birthday

What exactly does naskiĝtago mean? How is it formed, and is there any difference from a possible word like naskotago?

naskiĝtago is a compound word:

naskiĝ-i = to be born (intransitive)
tag-o = day

So naskiĝ-tago literally means “day of being born”, i.e. birthday.
This is the standard Esperanto word for birthday.

If you built nasko-tago from nask-i (to give birth, transitive), it would more naturally mean “day of giving birth”, i.e. the mother’s day of giving birth, which is not how we normally talk about a person’s birthday.

Therefore, for birthday, you should use naskiĝtago.

Why is it mia fratino without la? Shouldn’t it be la mia fratino for “my sister”?

In Esperanto, a possessive adjective (like mia, via, lia) usually replaces the definite article la:

mia fratino = my sister
via domo = your house
nia instruisto = our teacher

You normally do not say la mia fratino. That would sound strange in most contexts.

So mia fratino already means the sister that belongs to me, and it is definite enough without la.

Why does ideojn have -n, and why is there no article (“some ideas” vs “the ideas”)?

-n: In mi serĉas ideojn, the noun ideojn is the direct object of the verb serĉas (“to look for”). Direct objects take -n:
- Mi serĉas ideojn. = I look for ideas.
- Mi vidas la domon. = I see the house.
No article: We are talking about unspecified ideas, not particular ones already known. Esperanto has no separate word for “a / some”, so we just omit the article:
- mi serĉas ideojn = I look for (some) ideas
- mi serĉas la ideojn = I look for the (specific) ideas

Why is it en la interreto and not sur la interreto (“on the internet”) or just en interreto?

en = in / inside
sur = on (on the surface of something)

By convention, Esperanto speakers usually say:

en la interreto = in the internet (meaning on the internet)

We treat the Internet like a space or environment you are “in”, not a flat surface you are “on”.

About the article la:

la interreto = the Internet (the unique, global one people normally mean)
Bare interreto would mean “an internet / an internetwork” in a more technical or abstract sense, which is rare.

So the usual everyday expression is:

serĉi ideojn en la interreto = to look for ideas on the internet

What’s the difference between interreto and reto? Could I say en la reto instead?

Both are used:

interreto = specifically the Internet (global network)
reto = a network in general; by context it can also mean the Internet

In practice:

en la interreto and en la reto are both widely used to mean “on the Internet”.
Many speakers actually prefer the shorter la reto in everyday speech.

So yes, you could say:

Antaŭ la naskiĝtago de mia fratino mi serĉas ideojn en la reto…

Why does the sentence say legas unu retejon? What does unu add? Could we just say legas retejon?

unu is primarily the numeral “one”, but it can also suggest “one particular / a certain”.

legas unu retejon pri donacoj
= read one (particular) website about gifts (maybe out of several)

If you just say:

legas retejon pri donacoj

it usually means “read a website about gifts” in a more generic way. In many contexts this would sound more natural, because we typically read content (articles, posts) on websites rather than counting websites as objects we “read”.

So:

unu retejon: emphasizes it’s one specific website.
retejon without unu: a website, not emphasizing number.

Is legi retejon (“to read a website”) idiomatic in Esperanto, or should it be legi artikolon en retejo?

legi retejon is understandable and not wrong, but many speakers find it more natural to say what exactly you read on that website:

legi artikolon en retejo = to read an article on a website
legi priskribon de donacoj en retejo = to read a description of gifts on a website

So your sentence could also be:

… kaj legas artikolojn en unu retejo pri donacoj.
= … and read articles on one website about gifts.

Why is it pri donacoj and not pri donacojn?

pri = about, concerning
After a preposition like pri, nouns normally do not take -n, because they are not direct objects:
paroli pri donacoj = to talk about gifts
legi pri historio = to read about history

So:

retejo pri donacoj = a website about gifts

pri donacojn would only appear in rare, special cases with directional -n, which doesn’t apply here. The normal, correct form is pri donacoj.

Could the word order be different? For example, can I say Mi serĉas ideojn en la interreto antaŭ la naskiĝtago de mia fratino…?

Yes. Esperanto word order is fairly flexible. Your alternative is grammatically correct:

Mi serĉas ideojn en la interreto antaŭ la naskiĝtago de mia fratino kaj legas unu retejon pri donacoj.

The difference is mainly in emphasis:

Antaŭ la naskiĝtago de mia fratino mi serĉas…
→ Emphasizes the time frame (“Before my sister’s birthday, I do this…”)
Mi serĉas ideojn en la interreto antaŭ la naskiĝtago de mia fratino…
→ Starts with what you do, and adds the time information later.

Both are natural, but placing Antaŭ la naskiĝtago de mia fratino at the beginning highlights the “before the birthday” part.