La sonorilo ne funkciis hieraŭ, do mia amikino atendis kun sia pako antaŭ la pordo.

In Esperanto, -is marks the past tense.

• funkcias = works / is working
• funkciis = worked / was working

So La sonorilo ne funkciis hieraŭ means the bell or doorbell was not working yesterday.

Ne is the normal word for not, and it usually goes directly before the thing it negates.

So:

• ne funkciis = did not work

That placement is very regular in Esperanto, so learners quickly get used to it.

Do means so, therefore, or as a result.

It connects the two ideas:

• the bell was not working
• therefore, my friend waited outside

So do is showing the consequence of the first part of the sentence.

The suffix -in- marks a female person or animal.

• amiko = friend
• amikino = female friend

So mia amikino specifically means my female friend.

This is one of the most important Esperanto grammar points.

Sia is a reflexive possessive. It means his/her/their own, referring back to the subject of the clause.

In this sentence, the subject is mia amikino, so:

• sia pako = her own package

If you said ŝia pako, it would usually mean the package of some other woman, not the subject herself.

So:

• Mia amikino atendis kun sia pako = My female friend waited with her own package.

Yes, kun normally means with.

Here, kun sia pako means she was waiting with her package, in the sense that she had it with her or was carrying it.

So it does not mean the package was doing the waiting too; it simply tells you what she had with her while waiting.

Because pako is not the direct object here.

It comes after the preposition kun, and nouns after prepositions normally do not take -n unless there is a special idea of direction.

So:

• kun sia pako = with her package

No accusative is needed.

Because this sentence describes a location, not movement toward a place.

• antaŭ la pordo = in front of the door
• antaŭ la pordon would suggest movement to a position in front of the door

Since she was already waiting there, the location form is correct:

• atendis antaŭ la pordo = waited in front of the door

Some Esperanto time words are used directly as adverbs without needing an extra ending.

• hieraŭ = yesterday
• hodiaŭ = today
• morgaŭ = tomorrow

So hieraŭ already works as an adverb of time by itself.

Sonorilo is built from parts:

• sonor- = ring / sound
• -il- = tool or instrument
• -o = noun

So sonorilo literally means something like a ringing device or bell.

In this sentence, because of the context with the door, it most naturally means the doorbell.

La is the definite article, meaning the.

It is used when the speaker has a specific thing in mind. In this sentence, that makes sense:

• la sonorilo = the specific bell/doorbell at that place
• la pordo = the specific door there

Esperanto uses la a bit more straightforwardly than English: if it is definite, use la.

Esperanto word order is fairly flexible, but this sentence uses a very normal, natural order.

Current order:

• La sonorilo ne funkciis hieraŭ, do mia amikino atendis kun sia pako antaŭ la pordo.

You could move some parts for emphasis, for example:

• Hieraŭ la sonorilo ne funkciis...
• Antaŭ la pordo mia amikino atendis...

But the original version is clear and standard, which is usually best for learners.