Mi abbottono la camicia con calma prima della riunione.

Because Italian often uses a reflexive/pronominal construction for actions you do to your own body or clothing.

So mi abbottono la camicia is the natural Italian way to say I button my shirt.

Literally, it works a bit like I button myself the shirt, but you should translate it naturally into English, not word for word.

This pattern is very common:

• Mi lavo le mani = I wash my hands
• Si mette il cappotto = He/She puts on his/her coat
• Ci togliamo le scarpe = We take off our shoes

Here it means I button.

The full verb is abbottonarsi in this sentence, and mi abbottono is first person singular: I button up / I button my own shirt.

A useful comparison:

• io mi abbottono = I button my shirt
• loro mi abbottonano = they button my shirt

So abbottono is not they button. The they form would be abbottonano.

Because in Italian, when the owner is obvious, especially with body parts and clothing, you usually use the definite article instead of a possessive.

So Italian prefers:

• Mi abbottono la camicia
• Mi lavo i denti
• Si rompe il braccio

rather than constantly saying my shirt, my teeth, his arm.

Using la mia camicia is possible, but it usually adds emphasis, contrast, or clarification:

• Mi abbottono la mia camicia, non la tua

In a normal sentence, la camicia is the most natural choice.

Yes, in this sentence it is being used reflexively/pronominally: abbottonarsi.

The base verb is abbottonare, meaning to button.
With the pronoun, abbottonarsi means to button up oneself / to button one’s own clothing.

So:

• Abbottono la camicia = I button the shirt
• Mi abbottono la camicia = I button my shirt / I button up my shirt

The version with mi is especially natural when talking about getting dressed.

Because Italian usually leaves out subject pronouns when the verb form already shows who the subject is.

Abbottono already tells you the subject is I.

So Italian normally says:

• Mi abbottono la camicia

not:

• Io mi abbottono la camicia

You can add io for emphasis or contrast:

• Io mi abbottono la camicia, lui no

Con calma literally means with calm, but in natural English it means something like:

• calmly
• slowly
• without rushing
• taking my time

It is a very common Italian expression and often sounds more natural than a single adverb.

For example:

• Parla con calma = Speak calmly / Take it easy when you speak
• Facciamo tutto con calma = Let’s do everything calmly / without rushing

So in this sentence, it describes the manner of the action.

Yes, you could say Mi abbottono la camicia calmamente, and it is grammatically correct.

However, con calma is often more common and natural in everyday Italian. It can sound a little more conversational and idiomatic.

Very roughly:

• con calma = very common in speech
• calmamente = perfectly correct, but sometimes a bit more formal or stylistically marked

Because prima followed by a noun usually takes di.

So:

• prima di pranzo = before lunch
• prima della riunione = before the meeting

Here, di + la becomes della.

So the structure is:

• prima di + noun
• prima di + infinitive

Examples:

• prima della lezione = before the lesson
• prima di uscire = before going out

Yes. Italian word order is fairly flexible, although the original version is perfectly natural.

Possible variations include:

• Prima della riunione, mi abbottono la camicia con calma.
• Mi abbottono con calma la camicia prima della riunione.

The version you were given is neutral and clear:

• Mi abbottono la camicia con calma prima della riunione.

Changing the order can shift emphasis slightly, but not the basic meaning.