Postquam puella vestimenta plicavit et in armario posuit, ad bibliothecam rediit ut librum amissum quaereret.

Postquam means after and introduces a time clause.

So:

• Postquam puella vestimenta plicavit et in armario posuit = After the girl folded the clothes and put them in the wardrobe

It tells you that those actions happened before the next action:

• rediit = she returned

Latin often uses postquam with a verb in the perfect indicative to describe an action completed before the main action.

They are in the perfect indicative because they describe completed actions:

• plicavit = she folded
• posuit = she put

In this sentence, the folding and putting away happened first, and then she returned to the library. The perfect tense is a natural way in Latin to show those earlier, completed actions.

English sometimes uses simple past for this too, so folded and put are good translations.

Latin often leaves out subject pronouns when the verb ending already makes the subject clear.

For example:

• plicavit = he/she/it folded
• posuit = he/she/it put
• rediit = he/she/it returned

Because puella has already been named, Latin does not need to repeat ea or another pronoun for she. This is very normal in Latin.

Puella is nominative singular, which is the usual case for the subject of a sentence.

Here, puella is the one doing the actions:

• she folded
• she put
• she returned
• she searched

So puella is the subject of the whole sentence.

Vestimenta is accusative plural neuter here, because it is the direct object of plicavit.

• vestimentum = a garment
• vestimenta = clothes / garments

So:

• vestimenta plicavit = she folded the clothes

A native English speaker may expect clothes to behave like a plural-only word, but Latin simply uses the regular plural of vestimentum.

This is a very common Latin pattern:

• in + ablative often means in or inside a place
• ad + accusative often means to or toward a place

So:

• in armario = in the wardrobe / cupboard
• ad bibliothecam = to the library

The difference is about location versus motion toward:

• in armario = where the clothes ended up
• ad bibliothecam = where she went

Because in here expresses location: in the wardrobe.

When in means in/on in the sense of location, it usually takes the ablative:

• armarium = nominative/accusative singular
• armario = ablative singular

If in expressed motion into something, Latin often uses the accusative instead. But here the idea is that the clothes were placed and ended up in the wardrobe, so ablative makes sense.

Rediit comes from redeo, redire, redii/redivi, reditum, meaning to return or go back.

So:

• rediit = she returned

It is a perfect tense form, like she returned or she has returned, though in this sentence simple past is the natural English translation.

Learners often notice that it looks a bit different from more regular verbs. That is because redeo is a compound of eo (to go), which has some irregular forms.

Ut introduces a purpose clause here.

• ut librum amissum quaereret = in order to look for the lost book

So the structure is:

• rediit = she returned
• ut ... quaereret = so that she might search / in order to search

This tells you why she returned to the library.

Because after ut in a purpose clause, Latin normally uses the subjunctive.

So:

• ut ... quaereret = in order that she might look for / to look for

This is one of the most important uses of the subjunctive in Latin.

A learner can think of it this way:

• statement of fact: indicative
• purpose or intention: often subjunctive after ut

This is because of the sequence of tenses.

The main verb is:

• rediit = perfect tense, a secondary/historical tense

After a secondary tense, a purpose clause usually takes the imperfect subjunctive:

• quaereret

So Latin matches the subordinate verb to the tense sequence of the main verb.

A simple rule:

• primary tense in the main clause → often present subjunctive
• secondary/historical tense in the main clause → often imperfect subjunctive

That is why Latin has:

• rediit ut ... quaereret

not usually rediit ut ... quaerat

Librum amissum is accusative singular masculine.

• librum = book as the direct object
• amissum = lost, an adjective describing librum

The adjective must agree with the noun it modifies in:

• gender
• number
• case

So both are accusative singular masculine because together they mean:

• the lost book

And the whole phrase is the object of quaereret.

Either can work, depending on how natural you want the English to sound.

• quaero can mean seek, look for, search for, ask for, depending on context.
• Here, with librum amissum, it clearly means look for or search for.

So these are both good:

• to look for the lost book
• to search for the lost book

For most learners, look for is probably the most natural English choice here.

Latin word order is much more flexible than English word order because the endings show the grammatical relationships.

This sentence could be rearranged in various ways without changing the basic meaning, though the emphasis might shift.

For example, Latin can place:

• important words earlier for emphasis
• the verb later, often at the end of a clause
• adjectives either before or after nouns

In the given sentence, the order is quite clear and natural:

• time clause first: Postquam ...
• main action next: ad bibliothecam rediit
• purpose last: ut librum amissum quaereret

That order is elegant and easy to follow.