Before learning about the classification of accents in Spanish, let's first review some concepts about the accent: What is "accent"? Accent is the strength or intensity applied to a syllable when pronounced.

Another concept we can also review is "tilde". "Tilde" is the graphic mark we use on a vowel, as in "árbol" or "cajón". (Those short lines on vowels "a" and "o" are "tildes".)

Even Spanish speakers tend to talk about "tilde" using the term "acento". And this is not completely wrong, as "tilde" is the equivalent to "acento ortográfico", which is explained below.

So, in few words, the "acento" is the strength or intensity we apply to a syllable when we pronounced it, but "tilde" is the "graphic" mark.

We can say the word "alma" ("soul") is stressed on its syllable "al", but "alma" has no "tilde".

So, from this point, let's take a look at the different types of accentuation in Spanish: there are four different types:
- Accent "prosódico"
- Accent "ortográfico"
- Accent "diacrítico"
- Accent "enfático"

Acento prosódico
It is the pronounced accent, the pronunciation strength applied to the syllable. There is no visible mark on any vowel.
Examples: "la casa" - "la calle" - "la luna".

When we pronounce these three words (which correspond to the English "house", "street" and "moon", the strength is on their first syllable. But there are no written marks. All Spanish words, when pronounced, have the strength on one of their syllables, and that's the "prosódico" accent.
Note all words have "acento prosódico", as all words have a syllable pronounced with more emphasis.

Acento ortográfico
So, when a syllable has the strength when pronounced, that's the "acento prosódico". And when we, in addition, write a small line (´) on the vowel of that stressed syllable, that is, when we write a "tilde", that is the written accent or "acento ortográfico".

Some examples:
"el corazón" (the heart) - "la canción" (the song) - "la alegría" (joy)

Acento diacrítico
When we want to differentiate two words which spelling is exactly the same, but have different meanings, we need to write one of those words with "tilde" (´). For example, look at these words:

mas / más.
"más" means "more"
"mas" means "but"

tu / tú
"tu" means "your"
"tú" means "you"

si / sí
"si" means "if"
"sí" means "yes"

Acento enfático
Used in interrogative and exclamative sentences. That is, every question or exclamation includes interrogative / exclamative pronouns, and these pronouns always take a written accent (´), a "tilde", an "acento enfático".

For example:
¿Dónde va Ana? (Where is Ana going?)
¿Cómo te llamas? (What is your name?)

These two interrogative sentences include two interrogative pronouns: "dónde" and "cómo". These pronouns always taken the written accent.

¡Qué bonito" (So nice!)
This exclamative sentence includes the pronoun "qué", written with "tilde" as it is an exclamative sentence.

Main exclamative / interrogative pronounds are:
- cómo (how)
- quién (who)
- qué (what)
- dónde (where)
- cuándo (when)
- por qué (why)

The book Practice Makes Perfect Basic Spanish (Practice Makes Perfect Series) is an easy introduction to Spanish language. Learn the basics: Spamish articles, verb Ser and Estar or Spanish demonstratives.