Guarda la clau a la bossa, si no no pots obrir la porta.

Guarda is the informal singular imperative of guardar, so it means keep / put away / store when speaking to one person you address as tu.

So:

• guardar = to keep, to store, to put away
• guarda! = keep it / put it away!

In this sentence, Guarda la clau... is a command: Put the key in the bag or Keep the key in the bag.

One thing to notice: guarda can also be a present-tense form meaning he/she keeps or the formal you keep, but here the sentence clearly uses it as a command.

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

Here:

• pots = you can
• so Catalan does not need to say tu pots unless it wants extra emphasis

Likewise, the command guarda already implies you.

So the sentence naturally leaves out tu:

• Guarda la clau...
• ...no pots obrir la porta.

This is very normal in Catalan, just as in Spanish or Italian.

Catalan uses the definite article very often, sometimes more often than English does.

Here each noun is treated as a specific, known thing:

• la clau = the key
• la bossa = the bag
• la porta = the door

In context, these are not just any key, bag, or door, but particular ones that speaker and listener both understand.

Also, clau, bossa, and porta are all feminine singular nouns, so they take la.

This is a very common question. In Catalan, a can be used in places where English would use in, into, or inside.

So:

• Guardar la clau a la bossa = put/keep the key in the bag

With verbs like guardar, posar, and similar verbs of putting or placing, a is very natural.

Depending on context and region, you may also hear expressions with dins de for extra clarity:

• Guarda la clau dins la bossa
• Guarda la clau dins de la bossa

Those are more explicitly inside the bag, but a la bossa is perfectly normal.

Here si no means if not or more naturally in English, otherwise.

So:

• Guarda la clau a la bossa, si no no pots obrir la porta.
• Keep the key in the bag, otherwise you can’t open the door.

It is written as two words here because it really is:

• si = if
• no = not

That is different from sinó (one word, with an accent), which usually means but rather or except.

For example:

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

So in your sentence, si no is correct because it means if not.

Because the two no words are doing different jobs.

1. The first no is part of si no = if not / otherwise
2. The second no is the normal negation of the verb:
   • no pots = you cannot / you can’t

So:

• si no no pots obrir la porta
• literally: if not, you cannot open the door

This may look strange to an English speaker, but it is completely normal in Catalan.

Because after poder (to be able to / can), Catalan uses the infinitive of the next verb.

So:

• pots = you can
• obrir = to open

Together:

• pots obrir = you can open

This is the same pattern as in English:

• you can open not
• you can opens

So Catalan behaves very similarly here.

Pots is the second person singular present of poder:

• jo puc = I can
• tu pots = you can
• ell/ella pot = he/she can

In the sentence:

• no pots obrir la porta = you can’t open the door

Because the subject pronoun is omitted, pots by itself tells you the sentence is speaking to tu.

Here porta is a noun meaning door.

You can tell because it comes after the article la:

• la porta = the door

That said, porta can also be a verb form of portar (to carry / to wear / to bring), for example:

• Ella porta una jaqueta. = She is wearing a jacket.

So yes, porta can be either a noun or a verb in Catalan, but in your sentence la porta clearly means the door.

Yes. The meaning stays the same, but the punctuation can vary a little.

You may see:

• Guarda la clau a la bossa, si no no pots obrir la porta.
• Guarda la clau a la bossa; si no, no pots obrir la porta.

The second version separates the warning a bit more clearly. In writing, many people like a comma after si no:

• si no, no pots...

Word order can also change:

• Si no, no pots obrir la porta. Guarda la clau a la bossa.

But the original sentence is perfectly natural.

The command and the verb pots would change.

For formal singular (vostè):

• Guardi la clau a la bossa, si no no pot obrir la porta.

For informal plural (vosaltres):

• Guardeu la clau a la bossa, si no no podeu obrir la porta.

So the key changes are:

• guarda → guardi / guardeu
• pots → pot / podeu

No. Guardar is very natural, but Catalan also has other verbs depending on the exact nuance.

For example:

• desar also means to put away / store
• posar means to put

So you might also hear:

• Desa la clau a la bossa...
• Posa la clau a la bossa...

Very roughly:

• guardar suggests keeping it stored/safe
• posar focuses more on the act of putting
• desar often means put away

In your sentence, guardar works well because it suggests keep the key in the bag so you’ll have it when you need it.