Quan sortim per aquesta sortida, veiem una botiga on venen flors i xocolata.

Here quan means when, but in a sentence like this it often has a whenever / every time that sense too.

So Quan sortim per aquesta sortida, veiem... can be understood as a general or repeated situation:

• When / Whenever we go out through this exit, we see...

Catalan often uses the present tense with quan for things that happen regularly or are expected.

Catalan usually leaves out subject pronouns when the verb ending already shows who the subject is.

Here:

• sortim = we go out / we leave
• veiem = we see

Because those endings already mean we, adding nosaltres would usually only be for emphasis or contrast.

Sortim is the 1st person plural present indicative of sortir.

It means:

• we go out
• we leave
• in this context, something like we exit

The ending -im is very common for we forms of verbs like sortir.

Because per here means through / by way of.

So:

• sortir per la porta = to go out through the door
• sortir per aquesta sortida = to go out through this exit

For movement, per is very common when you mean the route or opening used to go through something.

Here sortida means exit.

It comes from the verb sortir (to go out / to leave), so the connection is very natural:

• sortir = to go out
• sortida = exit, way out

Be aware that sortida can also mean other things in different contexts, such as outing or way out, but here exit is the correct sense.

Because sortida is a feminine singular noun.

So the demonstrative has to agree with it:

• aquesta sortida = this exit

Compare:

• aquest llibre = this book
• aquesta porta = this door

Catalan adjectives, articles, and demonstratives usually agree in gender and number with the noun.

Yes, English might say When we go out through this exit, we will see..., but Catalan very often uses the present tense in this kind of sentence.

So:

• Quan sortim..., veiem...

sounds natural for:

• habitual actions
• predictable situations
• general observations

If you used a future form such as veurem, it could also work in some contexts, but the present here is very normal and idiomatic.

In this sentence, venen means they sell.

This is a very common point of confusion because:

• venen = they sell from vendre
• vénen = they come from venir

The written accent matters:

• no accent: venen = sell
• accent: vénen = come

So una botiga on venen flors i xocolata means a shop where they sell flowers and chocolate, not where flowers and chocolate come.

It is an unspecified they.

Catalan often uses the 3rd person plural when the speaker does not name the subject directly. English can do the same:

• They sell flowers there
• A shop where they sell flowers

In practice, it means something like:

• the people in the shop
• the shop
• people in general working there

So you should not look for a specific named subject in the sentence.

On means where.

It introduces a place clause:

• una botiga on venen flors i xocolata
• a shop where they sell flowers and chocolate

This is a very common use of on after a place noun:

• la casa on viu = the house where he/she lives
• el poble on vaig néixer = the town where I was born

Because the sentence is talking about the things the shop sells in a general way, not about specific flowers or specific chocolate.

So:

• venen flors i xocolata = they sell flowers and chocolate

This is natural when naming products, categories, or goods.

Also, xocolata is often treated as a mass noun here, like chocolate in English, so singular makes sense. Flors is plural because it refers to flowers as countable items.

Yes, it is very natural.

The sentence has:

1. a time clause first: Quan sortim per aquesta sortida
2. the main clause after it: veiem una botiga...

That order is common in Catalan, just as in English:

• When we go out through this exit, we see...

The comma is also normal after an opening clause like that.