According to the rules of the royal academy of the spanish language

ACCORDING TO THE RULES OF THE ROYAL ACADEMY OF THE SPANISH LANGUAGE

Within a word, the syllable on which the accent of intensity falls is the stressed syllable; the syllable or syllables pronounced with less intensity are unstressed syllables.

The accent of intensity can have a distinctive value depending on the syllable on which it falls. By example: hábito = habit / habito = inhabit / habitó = He - She inhabited.

To indicate the stressed syllable of a word, Spanish sometimes uses the accent graphic, also called tilde ( ´ ), sign placed on the vowel of the stressed syllable of the word according to well-established rules.

1. GENERAL RULES OF ACCENTUATION:

To correctly place the graphic accent in the words, it is necessary to follow the following general rules of accentuation:

1. ACUTE WORDS:
   They have the greatest voice force in the last syllable, they have a tilde in the stressed syllable when they end in a vowel (a, e, i, o, u) or consonants -n, -s.

Examples: cajón = drawer / comí = I ate / comerás = You´ll eat

*However, when the acute word ends in -s preceded by another consonant, it does not carry graphic accent.

Examples: robots = robots / tictacs = ticks

1. GRAVE WORDS:
   They have the greatest voice force in the penultimate syllable, they have a graphic accent on the stressed syllable when they end in consonant other than -n or -s.

Examples: ágil = agile / árbol = tree / álbum = album

* However, when the grave word ends in -s preceded by a consonant, it does have an accent.

Examples: bíceps = biceps / cómics = comics

* Grave words ending in "y" must have a tilde.
Examples: yóquey = yoquey

1.  THE WORDS ESDRÚJULAS:

They carry the greatest force of voice in the third to last syllable, they always carry a tilde in the stressed syllable.

Examples: indígena = indigenous / teléfono = telephone

1. THE WORDS SOBRE-ESDRÚJULAS:

They carry the greatest voice force in the third-third-to-last syllable, they always have an accent in the stressed syllable.

Examples: Dígamelo = Tell me / Cómetelo = Eat it

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1. DIACRITICAL TILDATION:

The diacritical mark is one that allows distinguishing, generally, words belonging to different grammatical categories, which nevertheless have the same form. By the tilde diacritical the words that are detailed below are distinguished.

1. DIACRITICAL MARK IN MONOSYLLABLES:

a) el = the / él = he

- el: Male article:
🡪 El conductor paró de un frenazo el autobús = Driver slammed the bus to a stop.

- él: Personal pronoun: 
🡪 Él me dijo = He told me.

b) tu = your / tú = you (singular)

- tu: possessive:
🡪 ¿Dónde has puesto tu abrigo? = Where have you put your coat?

- tú: personal pronoun:

🡪 Tú siempre dices la verdad = You always tell the truth.

c) mi = my / mi = noun MI / mí = me

- mi: possessive: 
🡪 Te invito a cenar a mi casa = I invite you to dinner at my house.

- mi: noun, with the meaning of  “musical note”: 
🡪 El MI ha sonado desafinado = MI has sounded out of tune.
- mí: personal pronoun:
🡪 ¿Tienes algo para mí? = Do you have something for me?

d) te = ¿? / té = tea

- te: personal pronoun:
🡪 Te compré unos zapatos = I bought you some shoes.

- té: noun, with the meaning of 'drink':

🡪 Toma una taza de té = Have a cup of tea.

e) mas = ¿? / más = more

- mas: adversative conjunction:
🡪 Él quizo convencerlo, mas fue imposible = He wanted to convince him, but it was impossible.

- más: adverb:
🡪 Habla más alto = Speak louder

f) si = if / si = noun SI / sí = yes / sí = himself

- si: conjunction:

🡪 Si llueve, no saldremos = If it rains, we will not go out. / ¡Cómo no voy a conocerlo, si lo veo todos los días! = How can I not meet him, if I see him every day!

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