Postquam domum redimus, mater rogat quid puellae in portu didicerint de gubernatore et de velo.

Because domum is one of the special Latin expressions for motion toward home. Latin often says domum ire, domum venire, domum redire without ad. The word domum here is accusative, but it works almost like an adverbial expression: home.

A useful set to remember is: domum = to home / home
domi = at home
domo = from home

The sentence is being told in the present tense as a narrative or general sequence of events: After we get home, mother asks... Latin can use postquam with the indicative, and here redimus is simply present indicative.

So postquam domum redimus means something like after we return home or once we get home. If the whole sentence were narrated in past time, you would expect different tense choices.

Postquam introduces a time clause meaning after. It sets the time for the main action. So the structure is:

Postquam domum redimus = the time/background
mater rogat = the main action

Latin often puts this kind of time clause first, just as English often does.

Because this is an indirect question, and quid is the interrogative word meaning what. After a verb like rogat, Latin uses an interrogative word such as quis, quid, cur, ubi, and so on.

Quod usually means something different, often because, which, or the fact that, depending on context. Here the sense is clearly what did the girls learn?, so quid is the right word.

It is called an indirect question because it depends on mater rogat rather than standing as a direct question by itself.

Direct question: Quid puellae in portu didicerunt?
= What did the girls learn in the harbor?

Indirect question: mater rogat quid puellae in portu didicerint
= mother asks what the girls learned in the harbor

In Latin, indirect questions normally use the subjunctive.

Because it is the verb of an indirect question. After a verb like rogat, Latin puts the verb of the indirect question into the subjunctive.

So: rogat quid... didicerint
means asks what they learned

If this were a direct question, the verb would be indicative instead: quid didicerunt?

Didicerint is the perfect subjunctive active, third person plural, from disco, discere, didici, meaning learn.

So it breaks down as:

• perfect stem: didic-
• subjunctive ending for third plural perfect active: -erint

It means they learned or they have learned, depending on context.

Because the learning happened before the mother asks about it. Latin uses the perfect subjunctive in an indirect question when the action is already completed relative to the main verb.

Here the sequence is:

1. the girls learn something in the harbor
2. mother asks what they learned

So didicerint shows prior, completed action. A present subjunctive would suggest something happening at the same time, which is not the idea here.

The form puellae can be several things: nominative plural, genitive singular, or dative singular. But the verb didicerint is third person plural, so it needs a plural subject.

That tells us puellae here must be nominative plural: the girls.

Because in with the ablative shows location, while in with the accusative shows motion into a place.

So: in portu = in the harbor
in portum = into the harbor

The girls learned something while they were located in the harbor, so Latin uses in portu, with the ablative.

Because they depend on de, and de takes the ablative.

So: de gubernatore = about the helmsman / pilot
de velo = about the sail

Whenever you see de, it is a good habit to expect an ablative noun after it.

Latin often repeats a preposition before each noun in a pair, especially when it wants the structure to be clear and balanced. So de gubernatore et de velo is completely normal.

Latin could sometimes leave the second de unspoken, but repeating it is very common and often sounds neater.

The sentence has three main parts:

Postquam domum redimus
= time clause introduced by postquam

mater rogat
= main clause

quid puellae in portu didicerint de gubernatore et de velo
= indirect question depending on rogat

So the whole sentence is built as: After we return home, mother asks [what the girls learned in the harbor about the helmsman and the sail].

Yes. Latin word order is much freer than English word order because the endings show how the words function. This sentence puts the time clause first, then the main verb, then the indirect question, which is a very natural arrangement.

But Latin could move things around for emphasis. For example, mater could appear later, or in portu could be moved closer to puellae or didicerint. The endings, not the position alone, tell you who is doing what.