No quiero sentarme en la fila de delante porque está demasiado cerca de la pantalla.

Because the verb here is sentarse, not sentar.

• sentar = to seat someone / to make someone sit
  
  • Voy a sentar al niño. = I’m going to seat the child.
• sentarse = to sit down
  
  • Voy a sentarme. = I’m going to sit down.

In your sentence, the speaker is talking about sitting down themselves, so Spanish uses the reflexive form sentarse.

Because when a reflexive verb is in the infinitive, the reflexive pronoun can be attached to the end.

So:

• No quiero sentarme
• No me quiero sentar

Both are correct and mean the same thing: I don’t want to sit down.

This happens a lot with infinitives in Spanish:

• voy a ducharme / me voy a duchar
• quiero acostarme / me quiero acostar

Spanish often leaves out subject pronouns when they are clear from the verb form.

• quiero already means I want
• so yo quiero is usually unnecessary

That is why No quiero sentarme... sounds natural.
You could say Yo no quiero sentarme..., but that adds emphasis, as if you were contrasting yourself with someone else.

It means the row in front or the front row / the row ahead, depending on context.

Literally, de delante means from/in the front or at the front. In this sentence, it refers to the row that is ahead of where the speaker would prefer to sit.

In Spain, la fila de delante is a very natural way to say the row in front.

Because delante often works as an adverb or adverbial expression, while de delante is commonly used as an adjective-like phrase to describe a noun.

Compare:

• La fila de delante = the row in front
• Está delante = it is in front

So:

• after a noun, Spanish often uses de delante, de atrás, etc.
• on its own, you often get delante, detrás

Yes, but the nuance changes a bit.

• la fila de delante = the row in front / the front row, depending on context
• la fila delantera = the front row / front-most row, more descriptive
• la primera fila = the first row

In a cinema context, la fila de delante sounds very natural in everyday speech in Spain.
If you specifically mean the very first row, la primera fila is the clearest.

Because porque is the conjunction meaning because.

• porque = because
• por qué = why

So:

• No quiero sentarme ahí porque está cerca. = I don’t want to sit there because it’s close.
• ¿Por qué no quieres sentarte ahí? = Why don’t you want to sit there?

This is a very common confusion for learners.

Because estar is used for location and for temporary states or conditions.

Here, está demasiado cerca de la pantalla means it is too close to the screen.
This is about position/location, so Spanish uses estar.

Compare:

• La fila está cerca de la pantalla. = The row is near the screen.
• Es grande. = It is big.
  Here ser describes an inherent characteristic.

The subject is understood from context: la fila de delante.

So the sentence means:

• I don’t want to sit in the front row because it is too close to the screen.

Spanish often leaves out the subject when it is obvious. Instead of repeating la fila de delante, it simply says está demasiado cerca...

Because cerca normally needs de before the thing it is near.

• cerca de la pantalla = near the screen
• cerca de casa = near home
• cerca del cine = near the cinema

So de is part of the standard pattern:

• cerca de
• lejos de

Here demasiado means too.

• demasiado cerca = too close
• demasiado tarde = too late
• demasiado caro = too expensive

It comes before the adjective or adverb it modifies. In this case, it modifies cerca.

So:

• está demasiado cerca = it is too close

Yes, in this context pantalla means screen, and because the sentence mentions a row, it strongly suggests a cinema, theatre, or similar venue.

Pantalla can also mean other kinds of screens, such as:

• a computer screen
• a TV screen
• a phone screen

But here, la pantalla is naturally understood as the big screen in front of the seats.

Yes. In Spain, la fila de delante sounds very natural and idiomatic.

A learner might also hear other variants in different regions, such as:

• la fila de adelante
• la fila delantera
• la primera fila

But for Spain, the original sentence sounds perfectly normal and everyday.