Esta tecla do teclado não funciona bem.

Because tecla is a feminine singular noun in Portuguese, so the demonstrative has to agree with it.

• esta = feminine singular
• este = masculine singular

So:

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

Portuguese uses gender agreement much more visibly than English does, so words like demonstratives and articles change form to match the noun.

Yes, you often could hear essa in Brazilian Portuguese.

Traditionally:

• esta = this (near the speaker)
• essa = that (near the listener, or a bit less close)

So in careful grammar, esta tecla means this key.

However, in everyday Brazilian Portuguese, many speakers use esse/essa very often, even in situations where traditional grammar would prefer este/esta. So all of these are possible depending on context and style:

• Esta tecla não funciona bem.
• Essa tecla não funciona bem.

The sentence with esta is completely correct and a bit more textbook/formal.

do teclado means of the keyboard.

It is made from:

• de = of/from
• o = the

These combine into the contraction:

• de + o = do

So:

• a tecla do teclado = the key of the keyboard / more naturally, the keyboard key

In Portuguese, this de + article structure is very common for showing possession or association.

Other examples:

• a porta do carro = the car door
• o fim do filme = the end of the movie

A little, yes — but it is still natural.

Since tecla already strongly suggests a keyboard key, many times a Brazilian speaker could simply say:

• Esta tecla não funciona bem.

Adding do teclado can help by making the context explicit, especially if the sentence is standing alone. It removes any possible doubt about what kind of key/button is being discussed.

So:

• Esta tecla não funciona bem. = natural
• Esta tecla do teclado não funciona bem. = also natural, just more explicit

There actually is an article there — it is hidden inside do.

• do = de + o
• o = the

So do teclado already includes the.

That means:

• tecla do teclado is literally
• key of-the keyboard

This kind of contraction is extremely common in Portuguese.

Some important ones:

• de + o = do
• de + a = da
• em + o = no
• em + a = na

Because in Portuguese, the normal place for não is before the verb.

So:

• não funciona = doesn't work

This is the standard pattern:

• Eu não sei. = I don't know.
• Ela não gosta. = She doesn't like it.
• O computador não liga. = The computer doesn't turn on.

English uses do/does not for many negatives, but Portuguese usually just puts não before the conjugated verb.

Literally, it means works well or functions well.

So:

• não funciona bem = doesn't work well

This is a very common way to talk about machines, devices, buttons, software, and similar things.

Examples:

• Meu mouse não funciona bem. = My mouse doesn't work well.
• O ar-condicionado funciona bem. = The air conditioner works well.

It suggests that the key works poorly, inconsistently, or not properly — not necessarily that it is completely dead.

Yes, but Portuguese often makes a distinction between:

• não funciona bem = doesn't work well
• não funciona = doesn't work

If the key is completely broken, não funciona is more direct.

If it works only sometimes, or you have to press it hard, then não funciona bem is especially appropriate.

Compare:

• Esta tecla não funciona. = It doesn't work at all.
• Esta tecla não funciona bem. = It works badly / unreliably.

Because Portuguese verbs already carry the person/number information, so you do not need a helping verb like does.

Here, funciona comes from the verb funcionar = to function / to work.

• funciona = it works

The subject is esta tecla, which is third-person singular, so the verb is in the third-person singular form.

English says:

• This key does not work well.

Portuguese says:

• Esta tecla não funciona bem.

No equivalent of English does is needed.

Yes. That would also be very natural, but it has a slightly different feel.

• não funciona bem = a general fact / usual problem
• não está funcionando bem = it is not working well right now / currently

So:

• Esta tecla não funciona bem.
  This key doesn't work well.
  → sounds like a general issue

• Esta tecla do teclado não está funcionando bem.
  This keyboard key isn't working well.
  → sounds more immediate or temporary

In everyday Brazilian Portuguese, the estar + gerund form is very common.

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

• funciona bem = works well

Putting bem after the verb is the most natural position here.

This is very common in Portuguese:

• Ele fala bem. = He speaks well.
• Ela dirige bem. = She drives well.
• O microfone funciona bem. = The microphone works well.

Yes. Tecla can mean a key or button, especially on devices.

For example:

• tecla do teclado = keyboard key
• tecla do elevador = elevator button
• tecla do controle remoto = remote-control button

That is one reason do teclado can be useful: it specifies exactly which kind of tecla you mean.

A natural Brazilian pronunciation would sound roughly like:

EH-sta TEH-kla du teh-klAH-du nang foon-syOH-na beng

A few notes:

• esta often sounds like EH-sta
• do is usually a short du
• teclado has stress on cla: teh-KLA-do
• não has a nasal sound that English does not have exactly
• bem also ends with a nasal sound in Brazilian Portuguese

The main stressed syllables are:

• ESta
• TEcla
• teCLAdo
• funciOna
• bem

Yes. In Brazilian Portuguese, direito is very common in this kind of sentence.

Compare:

• não funciona bem = doesn't work well
• não funciona direito = doesn't work properly

Both are natural. Direito often sounds a bit more colloquial and very common in spoken Brazilian Portuguese.

So you may hear:

• Esta tecla não funciona direito.

That means almost the same thing as the original sentence.