Ahir vaig anar a un restaurant prop de l'estació.

Catalan often drops subject pronouns when they are not needed, because the verb form already shows who the subject is.

• vaig = I
• so vaig anar already means I went

You could say Ahir jo vaig anar... if you want extra emphasis, but normally jo is omitted.

In this sentence, vaig anar is the periphrastic past, a very common Catalan past tense.

It is formed with:

• vaig
  • infinitive

So:

• vaig anar = I went

Even though vaig by itself comes from the verb anar (to go), in this structure it does not mean present tense. Together with the infinitive, it creates a past meaning.

For learners, it is best to memorize:

• vaig parlar = I spoke
• vaig menjar = I ate
• vaig anar = I went

Sometimes, but vaig anar is the most natural choice here, especially with ahir (yesterday), which refers to a finished past time.

In standard Central Catalan usage:

• ahir vaig anar... = the normal way to say yesterday I went...

he anat is the present perfect and is more often used when the action is connected to the present, though usage can vary by region.

So for this sentence, vaig anar is the safest and most natural form to learn.

Ahir means yesterday, and putting it at the beginning is very natural because it sets the time right away.

So:

• Ahir vaig anar a un restaurant...

is completely normal.

You can also move it:

• Vaig anar a un restaurant prop de l'estació ahir.

That is also understandable, but starting with ahir is often smoother and more common in this kind of sentence.

Because the verb anar normally takes a to show destination:

• anar a = to go to

So:

• anar a casa = go home
• anar a Barcelona = go to Barcelona
• anar a un restaurant = go to a restaurant

This is just the normal pattern of the verb.

Because un restaurant is indefinite: it means a restaurant, not the restaurant.

• a un restaurant = to a restaurant
• al restaurant = to the restaurant

Also, al is a contraction of:

• a + el = al

So if you were talking about a specific restaurant already known in context, al restaurant could be correct. But here the sentence means to a restaurant, so a un restaurant is right.

Prop de means near, close to, or nearby to.

It is a fixed expression:

• prop de casa = near home
• prop del mar = near the sea
• prop de l'estació = near the station

So in this sentence, it tells you where the restaurant was located.

Because in Catalan, the feminine singular article la becomes l' before a vowel sound.

So:

• la estació → l'estació

After de, you get:

• de l'estació = of/from the station

This apostrophe is very common in Catalan:

• l'escola
• l'amiga
• l'estació

Because the noun is simply feminine in Catalan:

• l'estació
• una estació

Grammatical gender in Catalan does not always match English, since English usually does not mark nouns as masculine or feminine. So this is something you usually just learn with the noun.

A good habit is to learn new nouns together with their article:

• l'estació, not just estació

Not completely. Catalan word order is fairly flexible, although some orders sound more natural than others.

The sentence here follows a very natural pattern:

• Ahir
  • vaig anar
    • a un restaurant
      • prop de l'estació

You could change the order for emphasis, for example:

• Vaig anar ahir a un restaurant prop de l'estació.

That is still correct. But the original version is a very good neutral model for learners.