Je vais au marché parce que les légumes y sont plus frais.

Because French usually conjugates the verb to match the subject.

• aller = to go (the infinitive, or dictionary form)
• je vais = I go / I am going

So in a full sentence, you normally need the conjugated form:

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

Aller by itself would only appear in structures like:

• Je veux aller au marché = I want to go to the market
• Aller au marché est utile = Going to the market is useful

Also, vais is an irregular form of aller, so it does not look much like the infinitive.

Because à + le contracts to au in French.

So:

• à + le marché → au marché

This is a standard contraction:

• à + le = au
• à + les = aux

Examples:

• Je vais au cinéma = I’m going to the cinema
• Je parle aux voisins = I’m speaking to the neighbors

Since marché is masculine singular, le marché becomes au marché after à.

The verb aller normally uses à before a destination.

• aller à Paris = to go to Paris
• aller au marché = to go to the market
• aller à la plage = to go to the beach

So Je vais au marché literally follows the pattern I go to the market.

English uses to, but French uses à and then applies contractions where needed.

Yes. Parce que is the standard, everyday way to say because.

• Je vais au marché parce que... = I go to the market because...

It introduces a reason.

You may also see car, which can also mean because, but it is often a little more formal or written in tone.

• Je vais au marché car les légumes y sont plus frais.

That is correct too, but parce que is the most common choice in ordinary speech.

Here, y means there.

In this sentence:

• les légumes y sont plus frais = the vegetables are fresher there

The y refers back to au marché.

So instead of repeating au marché, French uses y:

• Je vais au marché parce que les légumes au marché sont plus frais
  This is grammatical, but repetitive.
• Je vais au marché parce que les légumes y sont plus frais
  This is more natural.

So y is a pronoun that often replaces a place introduced by à, dans, chez, and similar ideas of location.

Not if you want to keep the same meaning and structure.

Without y:

• Je vais au marché parce que les légumes sont plus frais

This means I go to the market because the vegetables are fresher, but it no longer clearly says fresher there. The listener may still guess the meaning, but y makes the link to the market explicit.

So y is useful because it avoids repetition and makes the sentence more precise.

Because les légumes here means vegetables in a general, definite sense: the vegetables / vegetables in general in that place.

In this sentence, the speaker is talking about the vegetables at the market as a category:

• les légumes y sont plus frais = the vegetables there are fresher

If you said des légumes, it would sound more like some vegetables, which is not the idea here.

Compare:

• J’achète des légumes = I’m buying some vegetables
• Les légumes y sont plus frais = The vegetables there are fresher

So des is often used for an unspecified quantity, while les is used for a whole group or category.

Because the subject is plural:

• les légumes = the vegetables

Since les légumes is plural, the verb être must also be plural:

• les légumes sont = the vegetables are

Compare:

• Le légume est frais = The vegetable is fresh
• Les légumes sont frais = The vegetables are fresh

French verbs must agree with their subject in number and person.

In this sentence, frais agrees with les légumes, which is masculine plural.

The adjective frais has these common forms:

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

Since légume is masculine, and here it is plural (les légumes), the correct form is:

• les légumes sont frais

Then with plus:

• les légumes sont plus frais = the vegetables are fresher

So the adjective is already in the right agreeing form.

It means fresher.

French often forms the comparative with plus + adjective:

• plus frais = fresher
• literally: more fresh

This is completely normal in French.

Other examples:

• plus grand = bigger / taller
• plus intéressant = more interesting
• plus rapide = faster

So although the structure is literally more + adjective, the natural English translation is often the -er form when possible.

Because French object/location pronouns like y usually come before the conjugated verb.

So the structure is:

• subject: les légumes
• pronoun: y
• verb: sont
• comparative adjective: plus frais

That gives:

• les légumes y sont plus frais

This may feel different from English, where there often comes later:

• the vegetables are fresher there

But in French, pronouns such as y and en usually go before the verb:

• J’y vais = I’m going there
• Il en parle = He talks about it

It is present tense, but the French present tense can often translate in different ways in English depending on context.

• Je vais au marché can mean:
  • I go to the market
  • I am going to the market
  • I’m going to the market

In this sentence, both a habitual meaning and a current-action meaning are possible:

• habitual: I go to the market because the vegetables are fresher there
• immediate/current: I’m going to the market because the vegetables are fresher there

French uses the simple present more broadly than English does.

Y is pronounced like ee.

So:

• y sont sounds roughly like ee son

In natural speech, French rhythm connects the words smoothly:

• les légumes y sont plus frais

Also note:

• sont is pronounced like son
• the s in plus is often pronounced in plus frais, because plus is being used as a comparative

A rough pronunciation guide for the whole sentence could be:

• zhuh vay oh mar-shay parss-kuh lay lay-goom ee son plu fray

That is only approximate, but it may help at first.

Usually, au marché is the natural choice for to the market in this sentence.

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

If you say dans le marché, that usually emphasizes being physically inside the market.

Compare:

• Je vais au marché = I go to the market
• Je suis dans le marché = I am inside the market

So for destination with aller, au marché is the normal form.