Esta tecla do teclado não funciona bem.

Because tecla is a feminine noun in Portuguese.

• esta = this, for feminine singular nouns
• este = this, for masculine singular nouns

So:

• esta tecla = this key
• este teclado = this keyboard

The demonstrative has to agree with the noun in gender and number.

Tecla means a key on a keyboard, piano, keypad, etc.

In this sentence, tecla clearly means a keyboard key because of do teclado:

• tecla = key
• teclado = keyboard

So esta tecla do teclado means this key on the keyboard.

It can sound a little repetitive to an English speaker, but it is completely natural in Portuguese.

• do teclado literally means of the keyboard
• So tecla do teclado = key of the keyboard / keyboard key

Portuguese often uses this structure where English prefers a noun used as an adjective:

• tecla do teclado = keyboard key
• porta do carro = car door
• tela do computador = computer screen

So yes, the literal structure is different from English, but it is normal Portuguese.

Because de + o contracts into do.

This is one of the most common contractions in Portuguese:

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

So:

• a tecla do teclado literally = the key of the keyboard

You should think of do as a standard combined form, not as optional shortening.

Portuguese often uses the simple present where English may prefer the present continuous.

• não funciona bem literally = doesn’t function well
• In natural English, that often becomes isn’t working well

Both ideas are possible in Portuguese, but the simple present is very common for general current problems.

Compare:

• Esta tecla não funciona bem. = This key doesn’t work well / isn’t working well.
• Esta tecla não está funcionando bem. = This key is not working well.

The second version emphasizes the ongoing situation a bit more, but both are natural in Brazilian Portuguese.

Funciona bem means works well, functions properly, or works correctly.

• funcionar = to function, to work
• bem = well

So:

• funciona bem = works well
• não funciona bem = doesn’t work well / is not working properly

In this sentence, bem modifies the verb, not the noun.

Because bem is an adverb, and it modifies the verb funciona.

• bom/boa = good, as an adjective
• bem = well, as an adverb

Compare:

• O teclado é bom. = The keyboard is good.
• O teclado funciona bem. = The keyboard works well.

So here you need bem because the sentence is describing how it works, not what kind of thing it is.

Yes, absolutely.

If the context already makes it clear that you are talking about a keyboard, then do teclado is not necessary.

• Esta tecla não funciona bem. = This key doesn’t work well.
• Esta tecla do teclado não funciona bem. = This keyboard key doesn’t work well.

Adding do teclado makes it more explicit.

In Portuguese, não normally goes directly before the verb it negates.

So:

• funciona = works
• não funciona = does not work

This is the standard way to make a sentence negative:

• Eu entendo. = I understand.
• Eu não entendo. = I do not understand.

So não funciona bem is the normal word order for doesn’t work well.

In Brazilian Portuguese, não has a nasal sound and is roughly pronounced like nowng, but that is only an approximation.

Important points:

• the ã is nasal
• the final o is not pronounced like a strong English oh
• the whole word is usually one smooth nasal syllable

For many learners, the main challenge is making the vowel nasal. Listening and repeating native audio helps a lot here.

Grammatically, esta means this for a feminine noun near the speaker.

However, in everyday Brazilian Portuguese, the distinction between este/esta and esse/essa is often less strict than in formal grammar.

So in real speech, many Brazilians might also say:

• Essa tecla do teclado não funciona bem.

In many contexts, that would sound natural too. But esta tecla is grammatically correct and perfectly good Portuguese.

They are related words, but they mean different things:

• tecla = a key
• teclado = a keyboard

You can think of teclado as the whole set of keys, and tecla as one individual key.

Examples:

• A tecla Enter = the Enter key
• O teclado do computador = the computer keyboard

Yes. Funcionar is very commonly used for machines, electronics, systems, and even plans or methods.

Examples:

• O computador não funciona. = The computer doesn’t work.
• Meu celular funciona bem. = My phone works well.
• Essa ideia funciona. = That idea works.

So using funciona for a keyboard key is completely natural.