Mia fratino ne povis malfermi la pordon, ĉar mia frato jam ŝlosis ĝin kaj la seruro estis malnova.

The suffix -in- marks a female person.

• frato = brother
• fratino = sister

So fratino is built from frat- + -in- + -o.

No. Mia means my and does not change for gender.

So:

• mia fratino = my sister
• mia frato = my brother

However, like other Esperanto adjectives and possessives, it can change for number and accusative:

• mia = my
• miaj = my (plural)
• mian = my (accusative singular)
• miajn = my (accusative plural)

In this sentence, mia stays simple because both nouns are singular and not in the accusative.

In Esperanto, ne usually goes before the word or idea being negated.

• ne povis malfermi = could not open

This means the inability is being negated: she was not able.

If you said povis ne malfermi, that would mean something different, more like was able not to open or could choose not to open. So ne povis malfermi is the correct way to say could not open.

Because malfermi is an infinitive, meaning to open.

After modal verbs like povi (can / be able to), Esperanto uses the infinitive:

• povis malfermi = was able to open / could open

Only povis is conjugated for tense. The second verb stays in the infinitive.

Yes. Malfermi is built from fermi.

• fermi = to close
• malfermi = to open

The prefix mal- gives the opposite meaning. It is very common in Esperanto.

Other examples:

• bona = good → malbona = bad
• granda = big → malgranda = small
• juna = young → maljuna = old

So malfermi literally means to un-close.

Because la pordon is the direct object of malfermi.

Esperanto marks direct objects with -n:

• la pordo = the door
• la pordon = the door (as the thing being opened)

In this sentence, the sister is doing the action of opening, and the door is what she wanted to open, so pordo takes -n.

For the same reason: ĝin is also a direct object, so it takes -n.

• ĝi = it
• ĝin = it (object form)

Here ĝin refers back to la pordon.

So:

• mia frato jam ŝlosis ĝin = my brother had already locked it

Because pordo is a thing, not a person.

Esperanto uses:

• li for he
• ŝi for she
• ĝi for it

Since la pordon is a non-human noun, the correct pronoun is ĝin in the object form.

Esperanto has only one article: la, meaning the.

There is no separate indefinite article for a/an.

So:

• pordo can mean a door or just door, depending on context
• la pordo = the door

In this sentence, la pordon and la seruro refer to specific things, so la is used.

Jam means already.

• mia frato jam ŝlosis ĝin = my brother had already locked it

It usually goes before the verb or the part it most clearly modifies. Here it shows that the locking happened earlier, before the sister tried to open the door.

Esperanto word order is fairly flexible, but jam ŝlosis is very natural.

Because -is is the regular past-tense ending in Esperanto.

• povis = could / was able
• ŝlosis = locked
• estis = was

Esperanto verb endings are very regular:

• -as = present
• -is = past
• -os = future
• -us = conditional
• -u = command / wish
• -i = infinitive

So the sentence is easy to recognize as describing past events.

They are related, but not the same thing.

• pordo = door
• seruro = lock

So the sentence says she could not open the door, and one reason given is that the lock was old.

Ĉar means because. It introduces a reason.

So:

• Mia fratino ne povis malfermi la pordon, ĉar...
• My sister could not open the door, because...

The comma is normal before a subordinate clause like this, especially when it comes after the main clause. It helps separate the main statement from the explanation.

They each have a fixed pronunciation:

• ĉ = ch as in church
• ŝ = sh as in shoe
• ĝ = j as in judge

So in this sentence:

• ĉar sounds roughly like char
• ŝlosis begins with an sh sound
• ĝin begins with a j sound