Som al passadís de la verdura, prop de la caixa.

Som is the present-tense, first-person plural form of ser. Here it means we are.

Catalan usually leaves out the subject pronoun nosaltres because the verb ending already shows who the subject is. So Som... naturally means We are....

In Catalan, ser is very often used for simple location in everyday speech, especially in expressions like som aquí, ja som a casa, or som al supermercat.

So Som al passadís... is very natural. You may also hear estem in some varieties or contexts, but som is fully normal here and often sounds especially idiomatic when simply saying where someone is.

Al is the contraction of a + el:

• a + el = al

So:

• al passadís = in/to the aisle

This contraction is standard in Catalan. By contrast, a + la does not contract.

Literally, it means aisle of the vegetables / aisle of the produce.

Catalan often uses the pattern noun + de + noun where English prefers a noun used like an adjective:

• passadís de la verdura = vegetable aisle or produce aisle

So de links the aisle to the kind of products in that section.

Verdura is often used as a collective noun in Catalan. Even though English often says vegetables in the plural, Catalan can use singular verdura to mean vegetables, greens, or produce as a general category.

So la verdura here does not mean just one vegetable. It means the vegetable/produce section in general.

Prop de means near or close to.

Yes, the de is part of the expression when it is followed by a noun:

• prop de la caixa = near the checkout

So you would not normally say *prop la caixa.

You may also see a prop de, which means the same thing.

In a supermarket or shop, caixa usually means the checkout, cash register, or till.

Literally, caixa can also mean box, but in this context the shopping meaning is the natural one.

Catalan uses definite articles more often than English.

In this sentence:

• la verdura refers to the produce/vegetable category or section
• la caixa refers to the checkout area in the store

English often drops the article in similar phrases, but Catalan normally keeps it.

Yes. You could also say:

• Som prop de la caixa, al passadís de la verdura.

The original order is very natural because it first gives the main location the produce aisle and then adds another reference point near the checkout.

The comma simply marks a pause. The sentence would still be understandable without it.