Yo prefiero añadir moras al yogur, pero también me gustan los arándanos.

Because yo is optional here and adds a little emphasis or contrast.

Spanish often leaves subject pronouns out because the verb already shows who is doing the action:

Prefiero añadir moras al yogur...

is completely natural.

Including yo can make it feel more like:

As for me, I prefer...

In this sentence, yo slightly highlights the speaker’s personal preference before contrasting it with pero también...

Because the verb is preferir, and it is a stem-changing verb in the present tense.

The e in the stem changes to ie in most forms:

• yo prefiero
• tú prefieres
• él / ella prefiere
• nosotros preferimos
• vosotros preferís
• ellos / ellas prefieren

So prefiero is the correct yo form.

After a conjugated verb like prefiero, Spanish often uses an infinitive to express the action being preferred.

So:

Prefiero añadir moras al yogur

literally works like:

I prefer to add blackberries to yogurt.

This is very common in Spanish:

• Prefiero comer en casa.
• Quiero salir.
• Necesito estudiar.

You do not need de here. Prefiero de añadir would be incorrect.

Al is the contraction of a + el.

So:

• a el yogur becomes al yogur

This contraction is mandatory in normal Spanish.

Also, with añadir, Spanish typically uses a to mark the thing receiving what is being added:

• añadir azúcar al café
• añadir sal a la sopa
• añadir moras al yogur

So al yogur means to the yogurt.

In standard Spanish, yogur is a fully accepted and very common spelling. In Spain, this is the traditional recommended form.

You may also see yogurt sometimes, especially on packaging or influenced by English, but yogur is completely normal and standard.

Also, yogur is masculine in Spanish:

• el yogur
• al yogur

Because moras here refers to an indefinite amount or type of fruit, not to a specific set of blackberries already identified.

So:

añadir moras al yogur

sounds like:

to add blackberries to yogurt

in a general sense.

If you said añadir las moras al yogur, it would usually suggest specific blackberries that both speaker and listener already know about, like the blackberries.

This is a common difference in Spanish:

• no article for an unspecified quantity: comprar manzanas
• article for specific known ones: comprar las manzanas

Because gustar works differently from to like in English.

Spanish structures it more like:

Blueberries are pleasing to me.

So:

• me = to me
• gustan = are pleasing
• los arándanos = the blueberries

It is gustan because arándanos is plural.

Compare:

• Me gusta el yogur. = I like yogurt.
• Me gustan los arándanos. = I like blueberries.

Yo gusto los arándanos is incorrect for this meaning.

Because Spanish often uses the definite article when talking about things in a general class, especially with gustar.

So:

Me gustan los arándanos

means I like blueberries in a general sense.

This is very natural in Spanish. Similar examples:

• Me gustan las fresas.
• No me gustan los plátanos.
• Me encanta el café.

Without los, the sentence would usually sound less natural or more context-dependent.

In Spain:

• moras usually means blackberries
• arándanos usually means blueberries

A useful extra note: cranberries are often called arándanos rojos.

So in this sentence, the most likely meaning is:

• moras = blackberries
• arándanos = blueberries

The comma before pero is normal when pero links two full clauses:

• Yo prefiero añadir moras al yogur, pero también me gustan los arándanos.

This is similar to English punctuation before but.

As for también, it means also or too. It adds the idea that the second statement does not cancel the first one:

• I prefer blackberries, but I also like blueberries.

So the sentence means the speaker has a preference, but likes both.

Because of Spanish stress rules.

También has an accent because it is stressed on the last syllable, and words ending in n, s, or a vowel normally are stressed on the second-to-last syllable unless there is a written accent.

So the accent tells you to stress:

tam-BIÉN

Arándanos has an accent because it is stressed on the third-to-last syllable:

a-RÁN-da-nos

Words stressed on the third-to-last syllable always take a written accent in Spanish.

By contrast:

• prefiero needs no accent
• añadir needs no accent
• moras needs no accent
• yogur needs no accent

because their stress already follows normal spelling rules.