Learn Hardcore French: Nous y retournons demain, car le marchand y expose de nouvelles robes. - We are going back there tomorrow, because the merchant is exhibiting new dresses there.

In this sentence, y is a pronoun that replaces a previously mentioned or implied place introduced by à (or sometimes dans, sur, etc.). Here, it simply means there. So Nous y retournons translates as We’re going back there.

Why is y placed before the verb (retournons) rather than after it?

In French, object pronouns like y are placed immediately before a conjugated verb (in most tenses and moods). So in the present indicative you say nous y retournons, not nous retournons y. Note: in the affirmative imperative you would attach it after the verb (e.g. Retourne-y demain !).

Why is retournons in the present tense even though the action happens tomorrow? Could we use the future tense?

French often uses the present tense with a time adverb (here demain) to express what English calls the “near future.” It’s perfectly natural to say Nous y retournons demain instead of Nous y retournerons demain. Both are correct, but the present + time expression sounds more immediate or conversational.

What is the difference between car and parce que in …car le marchand y expose…?

Both car and parce que mean because, but they behave differently:

car is more formal or literary, and it never comes at the very beginning of a sentence. It simply links two statements in writing or formal speech.
parce que is the common spoken form to introduce a reason and can appear at the start of a clause.
Here car gives a slightly more formal or written feel: …, car le marchand y expose de nouvelles robes.

Why is it de nouvelles robes instead of des nouvelles robes?

When an adjective precedes a plural noun, the indefinite article des becomes de. Since nouvelles (new) comes before robes, you must say de nouvelles robes rather than des nouvelles robes.

There are two y pronouns in the sentence. Do they refer to the same thing?

Yes, both instances of y refer to the same location. The first marks where we are returning, and the second marks where the merchant is exhibiting the dresses. If the contexts were different, you might need to clarify, but here it’s the same place.

What does expose mean here? Is it the same as the English expose?

No false friend: expose in French means to exhibit or to display (as in an exhibit or showroom). It does not carry the English sense of to reveal secret information. So le marchand y expose de nouvelles robes means the merchant is exhibiting new dresses there.

Could we use on instead of nous? How would that change the tone?

Yes. Replacing nous with on is very common in spoken French:

On y retourne demain, car le marchand y expose de nouvelles robes.
This sounds more informal or conversational. Using nous is slightly more formal or emphatic.