Quando o teclado não funciona, eu uso o mouse para abrir o aplicativo do banco.

Quando means when, and it suggests a situation that happens from time to time or is expected to happen.

• Quando o teclado não funciona... = When the keyboard doesn’t work...
• Se o teclado não funciona... would mean If the keyboard doesn’t work...

In this sentence, quando sounds more natural because it describes what the speaker عادة does whenever that situation happens.

The comma separates the introductory clause from the main clause:

• Quando o teclado não funciona, = introductory time clause
• eu uso o mouse... = main clause

This is very similar to English:

• When the keyboard doesn’t work, I use the mouse...

In Portuguese, this comma is standard and natural here.

Both are possible, but they mean slightly different things.

• não funciona = doesn’t work / isn’t working properly in a general or simple sense
• não está funcionando = is not working right now, with stronger focus on the current moment

In your sentence, não funciona sounds simple and natural, especially for a routine statement:

• When the keyboard doesn’t work, I use the mouse...

If you wanted to emphasize the immediate situation, you could say:

• Quando o teclado não está funcionando...

Yes, it can be omitted.

Portuguese often drops subject pronouns when the verb already makes the subject clear:

• eu uso = I use
• uso also clearly means I use

So both are correct:

• Quando o teclado não funciona, eu uso o mouse...
• Quando o teclado não funciona, uso o mouse...

Including eu adds a little emphasis or clarity, but it is not required.

The present tense in Portuguese is often used for habitual actions, just like in English.

• eu uso o mouse = I use the mouse

Here it means:

• this is what I usually do
• this is my normal response in that situation

So the sentence describes a repeated or habitual action, not just one single event.

After para to express purpose, Portuguese normally uses the infinitive:

• para abrir = to open
• para estudar = to study
• para comer = to eat

So:

• uso o mouse para abrir o aplicativo = I use the mouse to open the app

Using a conjugated verb like para abro would be incorrect.

Because de + o contracts to do in Portuguese.

Common contractions:

• de + o = do
• de + a = da
• de + os = dos
• de + as = das

So:

• o aplicativo do banco = the bank’s app / the app of the bank

This contraction is required in normal Portuguese.

Literally, do banco means of the bank, but in natural English it usually means:

• the bank app
• the banking app
• the app from the bank

So o aplicativo do banco refers to the app belonging to or provided by the bank.

Portuguese uses definite articles more often than English.

Here:

• o teclado = the keyboard
• o mouse = the mouse
• o aplicativo = the app

Even when English might sound more natural without the in some contexts, Portuguese often keeps the article.

Also, all three nouns are masculine singular, so they use o.

Yes. In Brazilian Portuguese, people normally say mouse.

• o mouse is the standard everyday word
• rato is the literal translation of the animal rat/mouse, not the computer device in normal usage

So for a computer, mouse is the natural word in Brazil.

Yes, very often.

In Brazilian Portuguese, both are used:

• aplicativo = more formal/full version
• app = very common in everyday speech

So these are both natural:

• abrir o aplicativo do banco
• abrir o app do banco

The second one sounds a bit more casual and modern.

Because the subject is o teclado (the keyboard), which is singular.

• o teclado não funciona = the keyboard doesn’t work

Even though a keyboard has many keys, the noun itself is singular, so the verb is singular too.

If the subject were plural, the verb would change:

• As teclas não funcionam = The keys don’t work

Yes, somewhat. The original sentence is very natural:

• Quando o teclado não funciona, eu uso o mouse para abrir o aplicativo do banco.

You could also say:

• Eu uso o mouse para abrir o aplicativo do banco quando o teclado não funciona.

Both are correct. The original version emphasizes the situation first:

• When the keyboard doesn’t work...

That structure is very common and natural.

não has a nasal sound, which is very important in Portuguese.

It is roughly like nowng without a full final g, but that is only an approximation. The vowel is nasal, not a normal English vowel.

A few useful points:

• ã signals nasalization
• não is one of the most common words in Portuguese
• English speakers often pronounce it too clearly as two separate sounds; in Portuguese it is smoother and nasal

It is worth practicing because não appears constantly in everyday speech.

It most naturally describes a general habit or usual reaction.

• Quando o teclado não funciona, eu uso o mouse... = When the keyboard doesn’t work, I use the mouse...

This sounds like:

• whenever that problem happens, this is what I do

If you wanted to describe one specific moment happening right now, Portuguese would more likely use forms like:

• Como o teclado não está funcionando, estou usando o mouse...
• Quando o teclado não está funcionando, eu uso o mouse... depending on context

So the original sentence sounds habitual and general.