Si quieres, yo exprimo los limones y tú aplastas las patatas para la cena.

Si quieres literally means if you want.

Spanish often uses si + present indicative for real, possible conditions:

• Si quieres, ... = If you want, ...
• Si tienes tiempo, ... = If you have time, ...

Here it introduces a suggestion or offer, not a hypothetical unreal situation. That is why quieres is in the present indicative, not the subjunctive.

Yes, Spanish usually drops subject pronouns because the verb ending already shows who is doing the action:

• exprimo already means I squeeze
• aplastas already means you crush/mash

So the sentence could simply be:

• Si quieres, exprimo los limones y aplastas las patatas para la cena.

Including yo and tú adds contrast or emphasis, something like:

• I’ll squeeze the lemons and you mash the potatoes

It helps highlight the division of tasks.

They are both present tense forms:

• exprimo = I squeeze
• aplastas = you squeeze/crush/mash? No, here you crush/mash
• from the verbs exprimir and aplastar

More specifically:

• exprimir → yo exprimo
• aplastar → tú aplastas

Even though they are present tense forms, in this kind of context they can sound like an immediate plan or proposal in English:

• I’ll squeeze the lemons and you mash the potatoes

So Spanish often uses the present where English might prefer will.

Because the speaker is not directly giving two commands. The sentence sounds more like a suggestion, arrangement, or proposal.

Compare:

• Si quieres, yo exprimo los limones y tú aplastas las patatas
  = a cooperative plan

Versus imperatives:

• Exprime los limones y aplasta las patatas
  = direct commands

Using the present tense with si quieres makes it softer and more natural in this situation.

Spanish uses the definite article more often than English.

Here, los limones and las patatas refer to the lemons and potatoes involved in the cooking situation, so they are treated as known or understood items.

In English, you might say:

• I’ll squeeze the lemons and you mash the potatoes

Spanish keeps the articles:

• los limones
• las patatas

That is very normal.

In Spain, patatas is the usual word for potatoes.

In many parts of Latin America, people often say papas instead.

So for Spanish from Spain:

• las patatas = the potatoes

Both words are correct Spanish, but patatas is the more Spain-focused choice.

Literally, aplastar means to crush, flatten, or squash.

In a cooking context, with potatoes, it can be understood as to mash or crush them. So the meaning makes sense here.

That said, depending on the exact texture, Spanish speakers might also use other verbs such as:

• machacar = to crush/mash
• hacer puré = to make into purée / mash

So aplastar las patatas is understandable, though in some cooking contexts another verb might sound more idiomatic.

Para la cena means for dinner.

It expresses purpose or intended use: the lemons and potatoes are being prepared for dinner.

It applies to the whole activity, not just the potatoes:

• I squeeze the lemons and you mash the potatoes for dinner

Spanish often places this kind of phrase at the end, but it could be moved for emphasis.

The comma is natural because Si quieres is an introductory conditional phrase.

So this is the normal punctuation:

• Si quieres, yo exprimo los limones y tú aplastas las patatas para la cena.

In casual writing, people sometimes omit commas, but the comma is the best standard choice here.

Yes:

• Si quieres, exprimo los limones y aplastas las patatas para la cena.

That is completely grammatical.

The version with yo and tú just sounds more explicit and contrastive, especially if the speaker is dividing jobs between two people.

Tú is singular informal: one person, in an informal situation.

So aplastas is the second person singular form.

If you were speaking to more than one person in Spain, you would use vosotros:

• vosotros aplastáis

If you wanted a formal singular you, you would use usted:

• usted aplasta

Yes. Depending on context, si quieres can be translated as:

• if you want
• if you like
• if you’d like

In this sentence it softens the proposal, so in natural English it could feel like:

• If you like, I’ll squeeze the lemons and you can mash the potatoes for dinner.

So the exact English wording may vary, but the Spanish structure stays the same.