Mi malfermis la bankkonton ĉe la bankejo.

Because Esperanto often makes opposites with the prefix mal-.

• fermi = to close
• malfermi = to open

So malfermis literally means something like un-closed, but in normal English we translate it as opened. This is a very common Esperanto pattern:

• bona = good → malbona = bad
• granda = big → malgranda = small
• fermi = close → malfermi = open

In this sentence, malfermi bankkonton means to open a bank account, just as in English.

-is is the Esperanto ending for the past tense.

So:

• malfermas = opens / is opening
• malfermis = opened
• malfermos = will open

Since malfermis ends in -is, the action happened in the past: I opened.

The -n marks the direct object.

In the sentence:

Mi malfermis la bankkonton ĉe la bankejo.

the thing being opened is la bankkonton, so it gets -n.

Breakdown:

• Mi = I
• malfermis = opened
• la bankkonton = the bank account

Esperanto uses -n very regularly for direct objects, so this is something you will see constantly.

Because Esperanto often forms compounds by dropping the final -o of the first noun stem.

• banko = bank
• konto = account
• bankkonto = bank account

This is very normal in Esperanto compounds. The first part acts almost like a modifier.

Other examples:

• vaporŝipo = steamship
• lernejo = school
• dormoĉambro = bedroom

So bankkonto is the expected compound form.

ĉe usually means at, by, with, or in the vicinity of, depending on context.

In this sentence, ĉe la bankejo means something like:

• at the bank
• at the bank building
• at the banking place/branch

It often indicates being at someone’s place or at an institution.

For example:

• ĉe la kuracisto = at the doctor’s
• ĉe mia amiko = at my friend’s place

So here, ĉe is telling you where the account was opened.

Because ĉe and en are not exactly the same.

• en = in, inside
• ĉe = at, by, at the place of

If you say en la banko, you emphasize being inside the bank.
If you say ĉe la banko or ĉe la bankejo, you emphasize the bank as the place or institution where the action happened.

So:

• Mi malfermis bankkonton en la banko = I opened a bank account inside the bank
• Mi malfermis bankkonton ĉe la banko = I opened a bank account at the bank

In many situations, ĉe is the more natural choice for this kind of idea.

-ej- is a suffix meaning place for or place associated with something.

So:

• banko = bank
• bankejo = bank place, bank premises, bank establishment

A learner should know, though, that banko by itself already normally means the institution or bank building, so bankejo is understandable but can sound more marked or less usual than banko.

In many everyday situations, people would simply say:

Mi malfermis bankkonton ĉe la banko.

So bankejo is grammatically understandable, but banko is often more natural.

la is the Esperanto definite article, meaning the.

So:

• la bankkonton = the bank account
• la bankejo = the bank / the bank building

A useful point for English speakers: Esperanto has no indefinite article. There is no separate word for a/an.

So:

• bankkonto can mean a bank account
• la bankkonto means the bank account

Whether la is needed depends on whether the noun is definite in the context. If you are talking about a specific known account or a specific bank, la makes sense.

Usually yes, it is necessary.

Esperanto verbs do not change according to person:

• mi malfermis = I opened
• vi malfermis = you opened
• li malfermis = he opened

Because malfermis looks the same for all persons, the pronoun is usually needed to show who did the action.

Sometimes a pronoun can be omitted if the subject is obvious from context, but in a normal standalone sentence, Mi should stay.

Not completely. Esperanto word order is fairly flexible because endings like -n show grammatical roles.

The basic and most neutral order is:

Mi malfermis la bankkonton ĉe la bankejo.

But you could also say:

• Ĉe la bankejo mi malfermis la bankkonton.
• La bankkonton mi malfermis ĉe la bankejo.

These alternatives can change emphasis, but the standard subject–verb–object order is usually best for learners.

Yes. malfermi can be used both literally and figuratively.

So it can mean:

• to open a door
• to open a box
• to open a meeting
• to open a bank account

That works much like English open. So in this sentence, malfermis la bankkonton is a normal way to express opened the bank account.

ĉ is pronounced like the ch in church.

So ĉe sounds roughly like cheh.

A quick pronunciation guide for the sentence:

• Mi = mee
• malfermis = mahl-FER-mis
• la = lah
• bankkonton = bahnk-KON-ton
• ĉe = cheh
• la = lah
• bankejo = bahn-KEH-yo

The j in Esperanto is pronounced like English y, so -ejo sounds like EH-yo.