Guarda l'arxiu en una carpeta del teu ordinador, si no el pots perdre.

Guarda is the tu imperative form of guardar, meaning save or keep.

So Guarda l'arxiu... means Save the file...

A useful thing to notice is that in Catalan, the positive tu command often looks like the he/she/it present form:

• guardar → guarda
• parlar → parla
• escriure → escriu

So this is a direct instruction to one person.

Because arxiu begins with a vowel, the masculine singular article el becomes l' before it.

So:

• el llibre = the book
• l'arxiu = the file

This apostrophe is very common in Catalan and works much like contractions in other Romance languages.

They are two different computer-related nouns:

• arxiu = file
• carpeta = folder

So the sentence is telling you to save the file inside a folder.

En here means in.

So:

• en una carpeta = in a folder

The article una is used because it means a folder, not the folder. It is indefinite: any suitable folder, not a specific one already identified.

Del is the contraction of de + el.

• de = of / from
• el = the
• del = of the

So:

• del teu ordinador literally means of your computer

In more natural English, this would usually be understood as on your computer or on your computer’s system.

Also, Catalan normally uses the definite article with possessives:

• el teu ordinador = your computer
• not usually just teu ordinador

So del teu ordinador is completely normal Catalan.

No. This is a very common learner question.

Here, si no is two words and means if not or otherwise:

• Guarda l'arxiu..., si no el pots perdre.
• Save the file..., otherwise you might lose it.

By contrast, sinó as one word has a different meaning, usually but rather or except:

• No és blau, sinó verd.
• It isn’t blue, but rather green.

So in your sentence, si no must be written as two words.

That el is a direct object pronoun meaning it, referring back to l'arxiu.

So:

• el pots perdre = you can lose it

Catalan often uses object pronouns like this to avoid repeating the noun.

Yes. Both are possible.

With a conjugated verb plus an infinitive, Catalan often allows the object pronoun in two places:

• el pots perdre
• pots perdre'l

Both mean you can lose it.

The version in your sentence, el pots perdre, is perfectly normal.

Because arxiu is a specific masculine singular noun, so the matching direct object pronoun is el.

• l'arxiu → el

The pronoun ho is more neutral and usually refers to an idea, statement, or something not treated as a masculine/feminine countable noun.

So here:

• Guarda l'arxiu... si no el pots perdre = correct
• ...si no ho pots perdre = not the right choice for referring to arxiu

Literally, pots perdre means you can lose.

But in this kind of warning, English often translates it more naturally as:

• you might lose it
• you could lose it

So the sentence is not saying you definitely will lose it, but that losing it is a real possibility if you do not save it properly.