Postquam aquam hauserunt, ancilla et puella in cellam redierunt.

Postquam means after. It introduces a subordinate clause telling what happened first: Postquam aquam hauserunt = after they drew/fetched water.

Latin often puts this time clause first, but it does not have to. The sentence could be rearranged without changing the basic meaning.

Because aquam is the accusative singular of aqua.

Here, aquam is the direct object of hauserunt: it is the thing they drew or fetched. In Latin, direct objects normally go in the accusative case.

• nominative: aqua = water
• accusative: aquam = water, as the object of the verb

Hauserunt is the 3rd person plural perfect active indicative of haurio, haurire.

So it means they drew, they fetched, or they hauled up, especially of water.

The subject is understood from the verb ending -erunt, which here means they.

Because the real subject of hauserunt is still ancilla et puella. Latin often states the subject after the verb or even later in the sentence.

So the structure is:

• Postquam aquam hauserunt = after they fetched water
• ancilla et puella = the they, namely the slave-girl and the girl

Latin does not need to give the subject before the verb.

Because ancilla et puella is a compound subject: the slave-girl and the girl = two people.

Since the subject is plural in meaning, the verb is plural:

• redierunt = they returned

This is just like English: the maid and the girl returned, not returns.

Because in takes different cases depending on meaning:

• in + accusative = motion into or toward
• in + ablative = location in or inside

Here the girls are returning into the room/store-room, so Latin uses in cellam.

Compare:

• in cellam redierunt = they returned into the room
• in cella erant = they were in the room

Redierunt is the perfect tense of redeo, redire, meaning to go back or to return.

So redierunt means they returned.

This verb is built from:

• re- = back
• eo, ire = to go

So literally it has the idea of going back.

Both hauserunt and redierunt are in the perfect tense because the sentence is narrating completed past actions:

1. they fetched water
2. they returned to the room

In simple Latin storytelling, the perfect is very commonly used for events that happened and were completed.

Not always, but very often in straightforward narrative Latin, postquam is followed by a perfect verb when referring to a completed action in the past.

So Postquam aquam hauserunt is a very normal way to say After they had fetched water or simply After they fetched water.

Classical Latin has no definite article and no indefinite article. That means there is no separate word exactly like English the or a/an.

So:

• ancilla can mean a slave-girl or the slave-girl
• puella can mean a girl or the girl
• cellam can mean a room/store-room or the room/store-room

The context tells you which English article makes sense.

Yes. Latin word order is much freer than English because endings show the grammar.

For example, these would mean essentially the same thing:

• Postquam aquam hauserunt, ancilla et puella in cellam redierunt.
• Ancilla et puella, postquam aquam hauserunt, in cellam redierunt.
• In cellam redierunt ancilla et puella, postquam aquam hauserunt.

However, word order can change emphasis and style. The original order is a natural narrative order: first the earlier action, then the later one.

A cella is a small room, chamber, or often a store-room or pantry, depending on context.

So in cellam redierunt most likely means they went back into the room/store-room. The exact English word depends on the story’s setting.