Si no trobes l'ampolla, mira a la nevera.

Because after si meaning if, Catalan normally uses the present tense to talk about real future possibilities.

So:

• Si no trobes l'ampolla... = If you don’t find the bottle...

This is very similar to Spanish and different from English, which often uses present in the if clause too:

• If you don’t find it, ...

Using a future form after si would normally be incorrect here.

Trobes is the 2nd person singular present form of trobar, which means to find.

So:

• jo trobo = I find
• tu trobes = you find
• ell/ella troba = he/she finds

In this sentence, trobes matches an implied tu:

• Si no trobes l'ampolla...
• If you don’t find the bottle...

Because Catalan often drops subject pronouns when they are clear from the verb ending.

Here, trobes already tells you the subject is tu.
Likewise, mira here is a command to tu.

So Catalan usually prefers:

• Si no trobes l'ampolla, mira a la nevera.

rather than:

• Si tu no trobes l'ampolla, tu mira a la nevera.

You can include tu, but usually only for emphasis or contrast.

This is because of elision.

The feminine article la becomes l' before a word beginning with a vowel or silent h:

• la casa
• l'ampolla
• l'aigua
• l'hora

So:

• l'ampolla = the bottle

This works much like French elision.

Here mira is a command (the imperative) addressed to tu:

• mira = look
• in context: check / look in

So the sentence means:

• If you don’t find the bottle, look in the fridge.

Catalan often uses mirar in a practical sense like look/check.

Because the sentence is speaking to one person informally: tu.

Imperative forms vary depending on who you are addressing:

• mira = you, informal singular
• miri = you, formal singular
• mireu = you, plural

So this sentence is specifically:

• (tu) mira a la nevera

Literally, a la nevera means to the fridge or at/in the fridge, depending on context.

After mirar, Catalan often uses a when directing attention toward a place:

• mira a la nevera = look in/at the fridge

In natural English, we usually say look in the fridge, but Catalan uses a here.

So don’t translate the preposition too literally every time.

Yes, if you want to be more explicit about inside the fridge.

For example:

• Mira a la nevera = Look in/at the fridge
• Mira dins la nevera / Mira a dins de la nevera = Look inside the fridge

The original sentence sounds natural and idiomatic. The other versions just make the idea of inside more explicit.

No. Nevera is very common, but in some places you may also hear frigorífic.

In everyday speech:

• nevera = fridge
• frigorífic = refrigerator

In this sentence, nevera is the most natural everyday word.

The comma separates the if-clause from the main clause:

• Si no trobes l'ampolla, = if you don’t find the bottle
• mira a la nevera. = look in the fridge

This is the same idea as in English:

• If you can’t find the bottle, look in the fridge.

It helps make the structure clear and natural.

Yes, depending on context.

Literally, no trobes means you do not find. But in natural English, this often becomes:

• if you don’t find the bottle
• if you can’t find the bottle

Both can fit the Catalan sentence. The exact English wording depends on what sounds most natural in context.

It has two parts:

1. Si no trobes l'ampolla
   = If you don’t find the bottle

2. mira a la nevera
   = look in the fridge

So the pattern is:

• Si + present tense, imperative

This is a very common Catalan pattern for giving advice or instructions:

• Si tens gana, menja alguna cosa.
• If you’re hungry, eat something.

So your example is a useful model sentence.