Demain matin, je vais revenir au marché pour acheter des légumes frais.

Demain matin means tomorrow morning. French often puts time expressions at the beginning of a sentence to set the scene, just like English can do:

• Tomorrow morning, I’m going back to the market...

You could also place it later in the sentence, but starting with it sounds very natural.

Je vais revenir is the near future form, made with aller + infinitive.

• je vais = I am going to
• revenir = come back / return

So je vais revenir means I’m going to come back.

French uses this structure very often for future actions, especially in everyday speech. A more formal or simple future version would be:

• Je reviendrai au marché... = I will come back to the market...

Both are correct, but je vais revenir often sounds a bit more conversational.

Both revenir and retourner can relate to going back, but they are not always used in exactly the same way.

• revenir = to come back
• retourner = to go back / to return

In this sentence, revenir suggests coming back to a place the speaker has already been to. It works very naturally here.

So:

• Je vais revenir au marché = I’m going to come back to the market

A learner should know that in real French, both verbs may sometimes seem close, but revenir emphasizes returning, often from the speaker’s point of view.

Because à + le contracts to au in French.

So:

• à + le marché becomes au marché

This contraction is mandatory.

Other common contractions are:

• à + les → aux
• de + le → du
• de + les → des

So au marché simply means to the market.

After pour, French commonly uses the infinitive when the subject stays the same.

• pour acheter = in order to buy / to buy

In this sentence, the person who is going back to the market is also the person who will buy the vegetables, so French uses the infinitive:

• je vais revenir au marché pour acheter...

If the subject changed, French would usually need a different structure, often with pour que.

Here des is the normal plural indefinite article: some.

• des légumes = some vegetables

A common rule says des often becomes de before an adjective, but that usually happens when the adjective comes before the noun:

• des légumes frais = correct
• de bons légumes = correct

Why the difference?

• frais comes after the noun: légumes frais
• so des stays des

This is a very common point of confusion for learners.

Because frais agrees with légumes, which is plural masculine.

• singular masculine: frais
• singular feminine: fraîche
• plural masculine: frais
• plural feminine: fraîches

Since légumes is masculine plural, the correct form is frais.

Here frais means fresh in the sense of food that is not old, stale, or processed.

So:

• des légumes frais = fresh vegetables

It is a very common adjective with food:

• du pain frais = fresh bread
• du poisson frais = fresh fish

Yes, very much so. Demain matin is the normal way to say tomorrow morning.

Similarly, French often uses these simple time expressions:

• ce matin = this morning
• demain matin = tomorrow morning
• hier matin = yesterday morning

English speakers sometimes expect an article, but French does not use one here.

The comma separates the opening time expression from the rest of the sentence.

• Demain matin, je vais revenir...

It works like in English when you begin with something like Tomorrow morning, .... The comma is natural and helps readability, though punctuation can sometimes vary depending on style.

This sentence is already natural. In everyday speech, a native speaker might say it exactly like this:

• Demain matin, je vais revenir au marché pour acheter des légumes frais.

A few alternatives are also possible:

• Demain matin, je reviendrai au marché pour acheter des légumes frais.
  Slightly more formal or written.

• Demain matin, je retourne au marché pour acheter des légumes frais.
  Also natural, but with a slightly different verb choice.

So the original sentence is perfectly good everyday French.