Il compleanno di mia zia è a maggio, quindi le porto dei fiori.

In Italian, common nouns usually take an article more often than they do in English.

So:

• il compleanno = the birthday
• compleanno by itself would sound incomplete in a normal sentence like this

Here, compleanno is a singular masculine noun, so it takes il.

Italian often expresses possession with di:

• il compleanno di mia zia = the birthday of my aunt = my aunt’s birthday

This is a very normal Italian pattern:

• la macchina di mio fratello = my brother’s car
• il libro di Maria = Maria’s book

English often prefers ’s, but Italian usually uses di.

With singular family members, Italian usually drops the article before the possessive:

• mia zia = my aunt
• mio padre = my father
• mia sorella = my sister

So di mia zia is exactly what you would expect.

A useful contrast:

• mia zia = correct
• la mia amica = correct, because amica is not a family member

There are exceptions, such as when the family noun is modified:

• la mia zietta
• il mio caro fratello

Yes, a often means to or at, but with months Italian commonly uses a where English uses in:

• a maggio = in May
• a luglio = in July

So Il compleanno di mia zia è a maggio means My aunt’s birthday is in May.

You may also sometimes see in maggio, but a maggio is very common and natural.

Quindi means so, therefore, or thus.

It connects the two ideas:

• Her birthday is in May
• therefore / so I bring her flowers

It is showing a consequence or result.

Here le means to her.

The full idea is:

• porto dei fiori a mia zia = I bring flowers to my aunt

When Italian replaces a mia zia with a pronoun, it becomes:

• le porto dei fiori = I bring her flowers

So le is an indirect object pronoun.

In Italian, short object pronouns like mi, ti, gli, le, ci, vi, loro usually go before a conjugated verb.

So:

• le porto dei fiori = correct
• porto le dei fiori = not correct

Compare:

• Ti scrivo = I write to you
• Gli parlo = I speak to him
• Le porto dei fiori = I bring her flowers

Porto is present tense: I bring / I am bringing.

In Italian, the present tense is often used for:

• habits
• planned actions
• near-future actions

So le porto dei fiori can mean something like:

• I bring her flowers
• I’m bringing her flowers
• I bring her some flowers for that occasion

If you want to make the future more explicit, you could say:

• le porterò dei fiori = I will bring her flowers

Both can work, but the present tense is very common in everyday Italian.

Dei here is a partitive article, and it means some.

So:

• dei fiori = some flowers

This is very natural when you mean an unspecified quantity.

Compare:

• porto dei fiori = I’m bringing some flowers
• porto i fiori = I’m bringing the flowers (specific flowers)
• porto fiori = possible in some contexts, but more general or less natural here

So dei fiori is the best choice if you simply mean some flowers.

It can mean both, depending on context.

• portare una valigia = to carry a suitcase
• portare dei fiori a qualcuno = to bring someone flowers

In this sentence, porto dei fiori clearly means I bring flowers.

Yes. Le can also be the formal to you in Italian.

For example:

• Le porto un caffè could mean I’ll bring you a coffee when speaking formally to one person

But in this sentence, the context makes it clear that le refers to mia zia, so it means to her.