Quel film mi fa paura.

Because quel is the correct form of that before a masculine singular noun that starts with most consonants.

Film starts with f, so you use quel:

• quel film = that film

You use quello before masculine singular nouns beginning with:

• s + consonant: quello studente
• z: quello zaino
• gn: quello gnomo
• ps: quello psicologo
• x, y, etc.

So:

• quel film ✅
• quello film ❌

Because quel already functions as a demonstrative adjective meaning that, so you do not add a separate definite article.

Compare:

• il film = the film
• quel film = that film

You do not say:

• quel il film ❌

Mi means to me.

In this sentence, Italian uses an indirect object pronoun:

• mi = to me
• ti = to you
• gli / le = to him / to her
• ci = to us
• vi = to you all
• gli = to them

So Quel film mi fa paura is literally something like:

• That film makes fear to me

That literal wording sounds unnatural in English, but it helps explain why mi is there.

Fa is the third-person singular of the verb fare (to do / to make).

The subject is quel film, which is singular, so the verb must also be singular:

• quel film fa
• quei film fanno

So:

• Quel film mi fa paura = That film scares me / That film frightens me

Fare paura is a very common Italian expression meaning:

• to scare
• to frighten
• to be scary

Literally, it is to make fear, but idiomatically it means that something causes fear in someone.

Examples:

• Questo cane mi fa paura. = This dog scares me.
• I ragni mi fanno paura. = Spiders scare me.
• Mi fai paura. = You scare me.

So in your sentence, fa paura is the key expression.

They are very close, but not always identical in tone.

• Quel film mi fa paura = That film scares me / That film feels scary to me
• Quel film mi spaventa = That film frightens me

A useful way to think about it:

• fare paura often focuses on the feeling of fear something causes
• spaventare is a more direct verb meaning to frighten / to scare

In many everyday situations, either can work. But fare paura is extremely common and idiomatic in Italian.

Because mi is an unstressed object pronoun, and in Italian these pronouns normally go before the conjugated verb.

So:

• mi fa = it scares me
• ti fa = it scares you
• ci fa = it scares us

This is normal Italian pronoun placement.

Compare:

• Il cane mi spaventa.
• Quel rumore mi fa paura.

Usually, mi is the normal choice.

• Quel film mi fa paura. ✅

You can also say:

• Quel film fa paura a me.

But this usually adds emphasis or contrast, as if you mean:

• That film scares me
• ...maybe not other people, but me

You can also combine them for strong emphasis:

• Quel film a me fa paura.

So for a neutral sentence, mi is the most natural form.

Yes, Italian word order is fairly flexible, but the version you have is the most neutral and standard:

• Quel film mi fa paura.

You might also hear:

• Mi fa paura quel film.

This can sound more emphatic, as if the speaker is focusing on mi fa paura first, or identifying that film afterward.

Both are possible, but if you are learning the basic pattern, stick with:

• Subject + pronoun + verb + noun
• Quel film mi fa paura.

Yes, but it is not exactly the same.

• Quel film mi fa paura = That film scares me
• Quel film è pauroso = That film is scary

The first one emphasizes your reaction.
The second one describes the film itself.

So if you want to say that you feel fear, mi fa paura is often the better choice.

Yes, film is generally masculine:

• il film
• quel film

Its plural is usually unchanged:

• i film
• quei film

Examples:

• Quel film mi fa paura.
• Quei film mi fanno paura.

Notice that film stays the same, but the article/demonstrative and verb change:

• quel film fa
• quei film fanno

You change the pronoun and, if needed, the subject and verb.

Examples:

• Quel film ci fa paura. = That movie scares us.
• Quei film mi fanno paura. = Those movies scare me.
• Quei film ci fanno paura. = Those movies scare us.

Changes to notice:

• mi → ci
• quel film → quei film
• fa → fanno

This is a very useful pattern to practice.