In inverno porto un mandarino nello zaino per la merenda.

In inverno is the normal way to say in winter / during winter when you are speaking generally about the season.

Italian often uses in + season without an article for general time expressions:

• in inverno = in winter
• in estate = in summer
• in primavera = in spring
• in autunno = in autumn

Nell’inverno can exist, but it usually sounds more specific, like in that winter or during the winter of a particular year or situation.

So here, in inverno is the natural general expression.

Yes. In this sentence, portare means to carry / to take with you.

So porto un mandarino nello zaino means that I carry a mandarin in my backpack.

Be careful: portare can also mean to wear, depending on context:

• Porto uno zaino. = I’m wearing / carrying a backpack.
• Porto una giacca. = I’m wearing a jacket.

Here, because the object is un mandarino, the meaning is clearly carry / bring.

Because mandarino is a masculine singular noun that begins with a normal consonant sound, so it takes un.

Use:

• un before most masculine singular nouns:
  • un mandarino
  • un libro
  • un ragazzo

Use uno before masculine singular nouns beginning with:

• z
• s + consonant
• ps
• gn
• x
• y

For example:

• uno zaino
• uno studente
• uno psicologo

So:

• un mandarino
• but uno zaino

Because nello is the combination of:

• in
  • lo = nello

And zaino takes the masculine article lo, not il, because it begins with z.

So:

• lo zaino
• in + lo zaino → nello zaino

Compare:

• nel libro = in the book (in + il)
• nello zaino = in the backpack (in + lo)

This is the same pattern as:

• sullo scaffale = on the shelf
• dello studente = of the student

Masculine singular nouns in Italian usually take il, but some take lo instead.

Use lo before nouns beginning with:

• z
• s + consonant
• ps
• gn
• x
• y

Examples:

• lo zaino
• lo studente
• lo psicologo
• lo gnomo

Since zaino begins with z, it is:

• lo zaino
• uno zaino
• nello zaino

Here per la merenda means for snack / for my snack / to eat as a snack.

Per often expresses purpose or intended use. So the phrase tells you why the speaker is carrying the mandarin: it is meant to be eaten at snack time.

A few similar examples:

• porto un panino per il pranzo = I take a sandwich for lunch
• ho preparato un dolce per la festa = I prepared a dessert for the party

So per la merenda gives the purpose of the mandarin.

In Italian, meal or occasion words often appear with the definite article in expressions like this.

So:

• per la merenda
• per il pranzo
• per la cena

Even though English often says simply for snack or for dinner, Italian commonly uses the article.

Also, merenda is a feminine noun, so the article is la:

• la merenda

Yes. Italian uses the simple present tense for both:

1. what you do now
2. what you do regularly / habitually

So porto can mean:

• I carry
• I am carrying
• I usually carry

In this sentence, because of in inverno and the overall context, the present tense is understood as a habitual action: something the speaker generally does in winter.

This is very common in Italian.

Because Italian usually omits subject pronouns when they are not needed.

The verb form porto already tells you the subject is I:

• porto = I carry

So io porto is possible, but io is usually left out unless you want emphasis or contrast.

For example:

• Porto un mandarino... = neutral, normal
• Io porto un mandarino, non una mela. = I bring a mandarin, not an apple

This is one of the big differences from English.

Yes, Italian word order is flexible, although the original sentence is very natural.

Original:

• In inverno porto un mandarino nello zaino per la merenda.

Possible variations:

• Porto un mandarino nello zaino per la merenda in inverno.
• Per la merenda porto un mandarino nello zaino in inverno.

But the original order is good because it introduces the time first, then the action, then the details.

A rough structure is:

• In inverno = time
• porto = verb
• un mandarino = direct object
• nello zaino = place
• per la merenda = purpose

Italian often moves elements around for emphasis, but not every order sounds equally natural.

Yes, in this sentence it clearly means mandarin or mandarin orange.

The word mandarino can have other meanings in different contexts, but here the surrounding words make the fruit meaning obvious:

• it is something you can put nello zaino
• it is per la merenda

So there is no real ambiguity here.

Yes, d’inverno is also possible and means something like in winter / during the wintertime.

Compare:

• in inverno = very standard, straightforward
• d’inverno = also common, sometimes a bit more literary or stylistic depending on context

For a learner, in inverno is the safest and most neutral choice.