Se o técnico não aparecer amanhã de manhã, vou ligar para ele.

Because after se when you are talking about a possible future situation, Portuguese normally uses the future subjunctive.

So:

• Se o técnico não aparecer... = If the technician doesn’t show up...
• aparecer here is the future subjunctive form

This is very common in Portuguese:

• Se ele vier... = If he comes...
• Se chover... = If it rains...
• Se eu tiver tempo... = If I have time...

For many regular verbs, the future subjunctive looks the same as the infinitive, which is why aparecer looks unchanged.

Using não aparece here would sound wrong in standard Portuguese for this kind of future condition.

Here, aparecer means something like to show up, to appear, or to turn up.

In this sentence, it does not mean literally to appear visually. It means the technician is expected to come, and maybe he won’t arrive as planned.

So in this context:

• o técnico aparecer = the technician shows up / turns up

This is a very natural verb in Brazilian Portuguese for people who are expected somewhere.

Portuguese uses definite articles much more often than English does.

So o técnico is natural even when English would simply say the technician or sometimes just refer to the person by role.

In Portuguese, job titles and known people are very often introduced with an article:

• o médico
• a professora
• o técnico

Here, o técnico refers to a specific technician that both speaker and listener know about.

Not always. Técnico can mean different things depending on context.

In this sentence, it most likely means:

• a repair technician
• a service technician
• someone coming to fix/install/check something

But in other contexts, técnico can also mean:

• coach in sports
• technical specialist
• something technical as an adjective, depending on structure

So the exact meaning comes from context. In this sentence, it almost certainly refers to a person scheduled to come to the house or office.

Amanhã means tomorrow, but it does not specify the time of day.

So:

• amanhã = tomorrow
• amanhã de manhã = tomorrow morning

This is very natural in Portuguese. Similar expressions are:

• amanhã à tarde = tomorrow afternoon
• amanhã à noite = tomorrow evening / tonight, depending on context

So amanhã de manhã gives a more specific time frame.

Both are grammatically possible, but vou ligar is much more common in everyday Brazilian Portuguese.

• vou ligar = near future / very natural in speech
• ligarei = simple future, more formal or written-sounding in many contexts

So:

• Se o técnico não aparecer amanhã de manhã, vou ligar para ele.
  sounds very natural in conversation.

A version with ligarei is correct, but less conversational:

• Se o técnico não aparecer amanhã de manhã, ligarei para ele.

In Brazil, the ir + infinitive future is extremely common.

Yes, in this sentence ligar para ele means to call him.

The verb ligar has more than one meaning:

• ligar para alguém = to call someone
• ligar algo = to turn something on

So the preposition matters a lot:

• Vou ligar para ele. = I’m going to call him.
• Vou ligar o computador. = I’m going to turn on the computer.

Here, because of para ele, the meaning is clearly call him.

Because the verb in the sense of to call someone on the phone is commonly used as ligar para alguém in Brazilian Portuguese.

So the normal everyday pattern is:

• ligar para ele
• ligar para ela
• ligar para você
• ligar para o técnico

This is much more natural in Brazil than trying to use a direct object pattern.

You may also see pronoun forms like lhe, especially in more formal language or in other varieties of Portuguese, but in everyday Brazilian Portuguese, ligar para ele/ela/você is very common and natural.

Yes. That word order is also correct.

You can put the if-clause first or second:

• Se o técnico não aparecer amanhã de manhã, vou ligar para ele.
• Vou ligar para ele se o técnico não aparecer amanhã de manhã.

Both mean the same thing.

The version with se first may sound a little more organized or emphatic, because it sets up the condition before giving the result.

Also, when the se-clause comes first, the comma is normally used. When it comes second, the comma is usually omitted.

Yes, in standard writing, the comma is appropriate because the sentence begins with the conditional clause:

• Se o técnico não aparecer amanhã de manhã, vou ligar para ele.

That first part sets up the condition, and the comma separates it from the main clause.

If you reverse the order, you normally would not use a comma:

• Vou ligar para ele se o técnico não aparecer amanhã de manhã.

So the comma is connected to the sentence structure, not just to a pause in speech.

In standard Portuguese, não usually comes before the verb:

• não aparecer
• não vou
• não sei
• não chegou

So in this sentence, não aparecer is the normal word order.

You may hear other patterns in speech for emphasis in some contexts, but for learners, the safe and correct pattern is:

• não + verb

In Brazilian Portuguese, nh represents a sound similar to the ny sound in canyon, but smoother and as a single consonant.

So amanhã is approximately:

• a-ma-NYÃ

A few things to notice:

• the final ã is nasal
• the stress is on the last syllable
• nh is one sound, not n + h

Other words with nh:

• manhã
• tenho
• banho

For an English speaker, the nasal ending is often the trickiest part.

Yes, sometimes, but the nuance changes a little.

• aparecer = show up / turn up
• chegar = arrive

If you say:

• Se o técnico não chegar amanhã de manhã...

that focuses more on the technician’s arrival.

If you say:

• Se o técnico não aparecer amanhã de manhã...

that can sound a bit more like if he doesn’t show up as expected.

In many real-life situations, both would work, but aparecer often feels especially natural when someone may or may not come as arranged.

Yes, very much. This is a highly useful structure in Portuguese:

• Se + future subjunctive, [main clause]

You can reuse it in many everyday situations:

• Se ele não vier, eu aviso você.
• Se chover amanhã, vamos cancelar.
• Se eu tiver tempo, passo aí.
• Se ela ligar, me avise.

So this sentence is not just one isolated example. It teaches a very common Portuguese pattern for future possibilities and consequences.