Si no trobem el martell, el cargol i el tornavís, no podrem arreglar la bombeta ni l'aixeta avui.

Because in Catalan, after si meaning if in a real future condition, you normally use the present indicative, not the future.

So:

• Si no trobem... = If we don’t find...
• no podrem... = we won’t be able to...

This is very similar to English, which also says:

• If we don’t find it, we won’t be able to fix it
• not If we won’t find it...

So the pattern here is:

• si + present
• future in the main clause

Podrem is the future tense of poder (to be able to / can) for we.

So:

• poder = to be able to
• podrem = we will be able to

In the sentence:

• no podrem arreglar... = we won’t be able to fix...

A few related forms are:

• puc = I can
• pots = you can
• pot = he/she/it can
• podem = we can
• podrem = we will be able to

Because there are two separate negative clauses:

1. Si no trobem... = If we don’t find...
2. no podrem arreglar... = we won’t be able to fix...

Catalan normally puts no before the verb to make the clause negative.

So this is not redundant; each clause needs its own negation.

In negative sentences, ni often means nor or works like or under negation.

Here:

• no podrem arreglar la bombeta ni l'aixeta
  means
• we won’t be able to fix the light bulb or the tap
• or more literally, we won’t be able to fix the light bulb nor the tap

So ni is very natural after a negative verb.

Compare:

• Vull te o cafè = I want tea or coffee
• No vull te ni cafè = I don’t want tea or coffee

Yes. That would also be correct, and it gives a slightly stronger neither... nor... feel.

Compare:

• no podrem arreglar la bombeta ni l'aixeta
• no podrem arreglar ni la bombeta ni l'aixeta

Both are fine. The second version is a bit more explicitly parallel.

Catalan uses the definite article more often than English.

So where English might sometimes say:

• hammer, screw, and screwdriver

Catalan very naturally says:

• el martell, el cargol i el tornavís

This often happens when talking about specific, known objects in the situation.

So even if English might omit the in some contexts, Catalan usually keeps the article.

Because la becomes l' before a vowel sound.

So:

• la bombeta → starts with b, so it stays la
• la aixeta → this would sound awkward, so it becomes l'aixeta

This is called elision.

The same thing happens with masculine articles too:

• el martell
• l'armari

Yes. Cargol can mean both screw and snail.

Context tells you which meaning is intended.

In this sentence, because it appears with:

• el martell = the hammer
• el tornavís = the screwdriver

it clearly means screw, not snail.

This kind of double meaning is normal in many languages.

Yes, avui can go in different places, but the end of the sentence is very natural.

Here:

• no podrem arreglar la bombeta ni l'aixeta avui

means we won’t be able to fix the light bulb or the tap today.

You could also hear:

• avui no podrem arreglar la bombeta ni l'aixeta
• no podrem avui arreglar la bombeta ni l'aixeta

But the version with avui at the end sounds very normal and straightforward.

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

So the structure is:

• Si no trobem el martell, el cargol i el tornavís,
  if we don’t find the hammer, the screw, and the screwdriver,
• no podrem arreglar la bombeta ni l'aixeta avui.
  we won’t be able to fix the light bulb or the tap today.

This kind of comma is very common when a clause comes first.

The accent mark shows where the stress goes:

• tornavís

The stress is on the last syllable: -vís.

Without getting too technical, Catalan uses written accents to show stress when it does not follow the default pattern.

So the accent helps you pronounce it correctly.