Mi hermana prefiere la piña, pero yo me llevo una mandarina y unas cerezas al parque.

In Spanish, it is very common to use the definite article with foods when talking about likes, dislikes, or preferences.

So:

• Mi hermana prefiere la piña = My sister prefers pineapple

Here la piña does not necessarily mean one specific pineapple. It often means pineapple as a food / in general.

This is different from English, where we usually say just pineapple with no article.

A few similar examples:

• Me gusta el café = I like coffee
• Prefiero la pasta = I prefer pasta
• No me gusta el pescado = I don’t like fish

Prefiere is the third-person singular form of preferir in the present tense, because the subject is mi hermana.

• yo prefiero
• tú prefieres
• él / ella / usted prefiere

So:

• Mi hermana prefiere... = My sister prefers...

Also, preferir is a stem-changing verb, so the e in the stem changes to ie in most present-tense forms:

• preferir
• prefiero
• prefieres
• prefiere
• preferimos
• preferís
• prefieren

Yes, yo is often optional in Spanish because the verb already shows who the subject is.

So both of these are possible:

• pero me llevo una mandarina...
• pero yo me llevo una mandarina...

The version with yo adds emphasis or contrast. Here it helps create a contrast with mi hermana:

• Mi hermana prefiere la piña, pero yo...

So it sounds a bit like:

• My sister prefers pineapple, but I...

It highlights that the speaker is doing something different.

Me llevo comes from llevarse, which often means to take with oneself / to take away / to bring along.

In this sentence:

• yo me llevo una mandarina y unas cerezas al parque

it means something like:

• I’m taking a mandarin and some cherries to the park
• I’m bringing a mandarin and some cherries along to the park

The me does not mean myself in a literal English way here. It is part of the verb expression llevarse, which often suggests that the person is taking something along with them.

This is a very common question.

• llevo = I carry / I take
• me llevo = I take with me / I take away / I bring along

In many situations, both can be possible, but me llevo often sounds more natural when the speaker is taking something along as they go somewhere.

For example:

• Llevo una mochila. = I’m carrying a backpack.
• Me llevo una mochila al parque. = I’m taking a backpack with me to the park.

So in your sentence, me llevo emphasizes that the fruit is going with the speaker.

Because one item is singular and the other is plural.

• una mandarina = one mandarin
• unas cerezas = some cherries / a few cherries

So:

• una is the feminine singular indefinite article
• unas is the feminine plural indefinite article

Both mandarina and cerezas are feminine nouns, so they use una / unas.

It can mean either, depending on context.

In English, we often do not use an article here and simply say:

• I’m taking some cherries

In Spanish, unas cerezas often suggests some or a few cherries, not necessarily an exact number.

So this phrase is very natural for an unspecified small quantity.

Compare:

• llevo cerezas = I’m taking cherries / I take cherries
• llevo unas cerezas = I’m taking some / a few cherries

Because a + el contracts to al in Spanish.

So:

• a el parque becomes al parque

This is a standard contraction, just like:

• de + el = del

Examples:

• Voy al parque = I’m going to the park
• Vamos al cine = We’re going to the cinema
• Vengo del mercado = I’m coming from the market

One important note: this contraction does not happen with la.

• a la playa = correct
• not ala playa

Al parque means to the park.

The preposition a is used to show movement toward a place. Since the speaker is taking the fruit along to that destination, Spanish uses a:

• me llevo ... al parque = I take ... to the park

It tells you where the fruit is being taken.

Pero means but.

It connects two contrasting ideas:

• Mi hermana prefiere la piña
• pero yo me llevo una mandarina y unas cerezas al parque

The contrast is not necessarily a strong disagreement. It just shows a difference between what the sister prefers and what the speaker is taking.

So the sentence has the structure:

• My sister prefers X, but I’m taking Y...

Yes. The main verbs are in the present tense:

• prefiere = present
• me llevo = present

In Spanish, the present tense can describe:

1. A general fact or habit

   • Mi hermana prefiere la piña = My sister prefers pineapple

2. A current or near-current action

   • yo me llevo una mandarina... can mean I’m taking a mandarin...

So depending on context, the second part may sound like:

• I take a mandarin and some cherries to the park or
• I’m taking a mandarin and some cherries to the park

Both are reasonable translations.

Yes, yo llevo una mandarina y unas cerezas al parque is grammatically possible.

But me llevo is often more idiomatic when you mean that you are taking something along with you.

So:

• llevo focuses more on carrying or taking
• me llevo often sounds more like I’m taking it with me

In this sentence, me llevo feels very natural because the speaker is going somewhere and bringing the fruit along.

Because the sentence is doing two different things:

• la piña refers to a food in a general sense after prefiere
• una mandarina y unas cerezas refer to specific items the speaker is taking

So:

• prefiere la piña = general preference
• me llevo una mandarina y unas cerezas = specific fruit items

This is a very common pattern in Spanish.

Compare:

• Prefiero el té = I prefer tea
• Me llevo un té = I’m taking a tea

The first is general; the second is specific.

Yes. Hermana means sister, so it is a feminine noun.

That is why:

• mi hermana = my sister

And that is also why the verb form is the one for she:

• Mi hermana prefiere...

The possessive mi does not change for masculine or feminine singular nouns:

• mi hermano = my brother
• mi hermana = my sister

So mi works for both.

Almost nothing would change.

The sentence would still be:

• Mi hermana prefiere la piña, pero yo me llevo una mandarina y unas cerezas al parque.

That is because:

• yo does not change for gender
• me llevo does not change for gender
• the fruit words keep their own grammatical gender

Spanish verbs usually do not change depending on whether the speaker is male or female.

Only some adjectives or past participles used as adjectives would show gender, but there are none here.