Avui vaig al mercat perquè necessito fruita i roba.

Yes, this is a very common point of confusion.

In Catalan, vaig can appear in two different patterns:

• vaig
  • place / phrase = usually present tense of anar (to go)
    
    • Avui vaig al mercat = Today I go / I’m going to the market
• vaig
  • infinitive = the periphrastic past, very common in Catalan
    
    • Vaig anar al mercat = I went to the market

So in Avui vaig al mercat, there is no infinitive after vaig, so it is understood as the present tense I go / I’m going.

Catalan often leaves out subject pronouns because the verb ending already shows who the subject is.

• vaig = I go
• necessito = I need

So jo is not necessary unless you want emphasis or contrast:

• Avui vaig al mercat = Today I’m going to the market
• Avui jo vaig al mercat, no pas tu = Today I’m going to the market, not you

This is similar to Spanish and unlike English, where the subject usually has to be stated.

Al is the contraction of:

• a = to
• el = the

So:

• a + el = al

That means:

• al mercat = to the market

This contraction is required in normal Catalan.

Catalan normally uses the article in places where English often does too:

• vaig al mercat = I go to the market
• vaig al banc = I go to the bank
• vaig a l’escola = I go to school / the school depending on context

So mercat here naturally appears with the article el, which becomes al after a.

Here perquè means because.

The accent matters because Catalan distinguishes several similar-looking forms:

• perquè = because
• per què = why / for what reason
• per a què or perquè in some contexts can relate to so that, depending on structure and register

In your sentence:

• Avui vaig al mercat perquè necessito fruita i roba.
• Today I’m going to the market because I need fruit and clothes.

So this is the straightforward because form.

Necessito is simply the normal verb I need.

• necessitar = to need
• necessito = I need

It is the most direct and natural choice here:

• necessito fruita = I need fruit
• necessito roba = I need clothes

A phrase like tenir necessitat de exists, but it is much less common and sounds more formal or abstract.

Because fruita and roba are being used in a general, indefinite sense.

• fruita = fruit
• roba = clothes / clothing

So:

• necessito fruita i roba = I need fruit and clothes

If you added articles, the meaning would change:

• necessito la fruita = I need the fruit (specific fruit)
• necessito la roba = I need the clothes (specific clothes)

Without the article, it means fruit and clothes in general.

In this sentence, roba means clothes or clothing.

This can feel strange to English speakers because it looks a bit like robe or something related to fabric, but in normal Catalan:

• roba = clothes / clothing

Examples:

• Compro roba nova = I buy new clothes
• Necessito roba d’hivern = I need winter clothes

Here fruita is a mass or collective noun, much like fruit in English.

• fruita = fruit in general
• fruites = fruits / different pieces or kinds of fruit, depending on context

So:

• necessito fruita = I need fruit
• necessito fruites tropicals = I need tropical fruits

Using the singular here is the most natural general expression.

The sentence is in the present indicative.

• vaig = present of anar (to go)
• necessito = present of necessitar (to need)

Even though English might often say I’m going to the market today, Catalan can simply use the present tense for a planned or current action:

• Avui vaig al mercat = Today I’m going to the market

This is very natural.

Yes. Catalan word order is flexible, although some orders sound more natural than others depending on emphasis.

Your sentence:

• Avui vaig al mercat perquè necessito fruita i roba.

Possible alternatives:

• Vaig al mercat avui perquè necessito fruita i roba.
• Perquè necessito fruita i roba, avui vaig al mercat.

Putting Avui at the beginning is very natural because it sets the time right away.

A simple learner-friendly pronunciation guide would be:

• perquè ≈ per-KEH

The stressed syllable is the last one because of the accent:

• per-QUÈ

The accent mark shows where the stress falls and helps distinguish it from other similar forms.

Yes, i is the normal Catalan word for and.

• fruita i roba = fruit and clothes

Unlike Spanish, where y sometimes changes to e before an i sound, Catalan normally just keeps i.

So this is straightforward:

• pa i formatge = bread and cheese
• fruita i roba = fruit and clothes

Yes. Even though the Catalan sentence does not explicitly say some, English often adds it naturally in translation.

• necessito fruita i roba can mean
  I need fruit and clothes
  or
  I need some fruit and some clothes

Catalan often leaves this kind of quantity unspecified unless it needs to be precise.

Mercat means market, and in many everyday contexts it often suggests a place where people buy food, fresh produce, and household items.

So in this sentence:

• vaig al mercat perquè necessito fruita i roba

it sounds like the speaker is going to a market where both food and clothes might be sold. That is perfectly natural in Catalan-speaking contexts, especially for traditional markets.