Q:

a spectacular vs an spectacular

Is it:

a spectacular movie

or it is said:

an spectacular movie

I'm writing a book in English but I'm Latino so I might need some help with this, I'd appreciate it a lot 

A:

The indefinite article "an" is used in front of words that have an initial vowel sound regardless of whether the first letter be a vowel or not. This is called a "sandhi" in English, which is similar to a liaison in French and other Romance languages. In fact, "sandhi" is the catchall term whereof a liaison is a subcategory.  
So ask yourself this question: does the word "spectacular" begin with a vowel sound?  Is the sibilant "s" a vowel sound?  The answer is no, it is not; therefore, the answer is:

a spectacular movie

Notice words that do take "an" usually have a vowel as their first letter, but this is not always the case because of the pronunciation.  There are some that can also take both depending upon the pronunciation that the speaker uses.

a book, a doll, a worm, an hour, an apple, a boy, an octopus, a/an
  historic occasion, a/an hotel, a briefcase, a raisin, an engineer, a
  user, a board, an orange.

I hope that might have helped you out.  Take care and good luck.

A:

It is "a spectacular movie"
An is only used when the noun starts with a vowel sound.  

An opera, an artichoke

Note that even if the word starts with a vowel, but sounds as a consonant, it will not use an:

a one-time event.

The 'w' sound of one does not need an 'an' (while this example does...)

