La fioraia regala un mazzo di tulipani alla bibliotecaria, che lo mette subito in acqua.

Italian usually uses articles more often than English.

• la fioraia = the florist
• la bibliotecaria = the librarian
• alla bibliotecaria = to the librarian

Here, alla is actually two words combined:

• a = to
• la = the

So:

• a + la = alla

Even when English might say to a librarian or just to librarian in some contexts, Italian normally wants the article here.

Fioraia means florist and refers here to a female florist.

The ending -a is the usual feminine singular ending in Italian for many nouns and adjectives.

Compare:

• il fioraio = the male florist
• la fioraia = the female florist

The same pattern appears in:

• il bibliotecario = the male librarian
• la bibliotecaria = the female librarian

So the sentence is specifically talking about two women.

Un mazzo di tulipani means a bunch/bouquet of tulips.

Italian often uses mazzo di to talk about flowers gathered together as a gift. So:

• un mazzo = a bouquet / bunch
• di tulipani = of tulips

This is more natural than simply saying regala tulipani if you want to emphasize the gift as a bouquet.

Here di means of, not some.

• un mazzo di tulipani = a bouquet of tulips

This is a structure of quantity or composition: [noun] + di + [thing].

Other examples:

• un bicchiere di acqua = a glass of water
• una tazza di caffè = a cup of coffee
• un gruppo di amici = a group of friends

If you said dei tulipani, that would more likely mean some tulips, which does not fit the structure after mazzo.

Regala is the third-person singular present tense of regalare, meaning to give as a gift.

Conjugation:

• io regalo
• tu regali
• lui/lei regala
• noi regaliamo
• voi regalate
• loro regalano

Since the subject is la fioraia = she, the verb is regala.

Italian often uses the present tense in situations where English also uses the present:

• La fioraia regala... = The florist gives/is giving...

Both can relate to giving, but they are not identical.

• dare = to give
• regalare = to give as a present / to gift

So regala un mazzo di tulipani suggests that the bouquet is a gift, not just something being handed over.

Compare:

• dà un libro a Marco = gives Marco a book
• regala un libro a Marco = gives Marco a book as a gift

Because the librarian is the recipient of the action.

The florist gives the bouquet to the librarian, so Italian uses the preposition a:

• regalare qualcosa a qualcuno = to give something to someone

Pattern:

• La fioraia = subject
• regala un mazzo di tulipani = verb + direct object
• alla bibliotecaria = indirect object, the person receiving the gift

So:

• un mazzo di tulipani is what is given
• alla bibliotecaria is the person it is given to

Here che means who.

It introduces a relative clause that gives extra information about la bibliotecaria:

• alla bibliotecaria, che lo mette subito in acqua
• to the librarian, who immediately puts it in water

So che can mean:

• that
• who
• which

depending on what it refers to.

In this sentence it refers to a person, so in English we translate it as who.

Because of the meaning and the verb that follows.

The clause is:

• che lo mette subito in acqua

The pronoun lo means it and refers to un mazzo. So the person doing the action of putting it in water must be someone else: the librarian.

In other words:

• che = the librarian, who...
• lo = the bouquet, it

So the structure is:

• the florist gives a bouquet to the librarian,
• who immediately puts it in water.

Lo is a direct object pronoun meaning it, referring to un mazzo di tulipani.

Since mazzo is a masculine singular noun, the pronoun is lo.

Compare:

• masculine singular: lo = it / him
• feminine singular: la = it / her
• masculine plural: li = them
• feminine plural: le = them

Examples:

• il libro → lo
• la penna → la
• i libri → li
• le penne → le

So:

• un mazzo is masculine singular
• therefore lo mette = puts it

In Italian, object pronouns usually come before a conjugated verb.

So:

• mette il mazzo in acqua = puts the bouquet in water
• lo mette in acqua = puts it in water

This is very normal Italian word order with pronouns.

Compare:

• Vedo Marco → Lo vedo
• Compra la mela → La compra
• Prende i libri → Li prende

So lo mette is the standard order, not mette lo.

Yes, that would also be grammatical.

• che mette subito il mazzo in acqua = who immediately puts the bouquet in water
• che lo mette subito in acqua = who immediately puts it in water

Using lo avoids repeating un mazzo di tulipani, so it sounds more natural and less repetitive.

Italian often prefers a pronoun when the noun has just been mentioned and is already clear.

Subito means immediately or right away.

In the sentence:

• che lo mette subito in acqua

it modifies the verb mette and tells us that the librarian acts at once.

Italian adverbs like subito are fairly flexible in position. You may hear:

• lo mette subito in acqua
• subito lo mette in acqua
• lo mette in acqua subito

But the version in the sentence is very natural.

Both can be possible, but they are not exactly the same in feel.

• mettere in acqua = to put in water
• mettere nell’acqua = to put into the water

With flowers, mettere in acqua is a very common idiomatic expression. It means putting them into water so they stay fresh.

It works a bit like English put in water, where we do not always need the.

Yes, it helps show that the relative clause adds extra information.

• alla bibliotecaria, che lo mette subito in acqua

The comma suggests a non-restrictive idea in writing: we are talking about the librarian, and then adding extra information about what she does next.

Without the comma, the sentence would look more tightly connected, though in everyday Italian you may still see variation. In this sentence, the comma makes the sequence of actions very clear.

Yes. Italian can replace alla bibliotecaria with the indirect object pronoun le.

So you could have:

• La fioraia le regala un mazzo di tulipani = The florist gives her a bouquet of tulips

Here:

• le = to her

If the person has already been identified, using le is very natural. The original sentence spells out alla bibliotecaria to make everything explicit.