PHONETIC STRESS AND ACCENT MARKS
Spanish words have only one phonetic stress. The stress is marked with a written accent ( ´ ) according to the following rules:
Words stressed in the last syllable have a written accent on it only if the last letter ends in "n", "s", or vowel. These words are named "agudas".
Words stressed on the next to last syllable need an accent on it if the last letter is any consonant, except "n" or "s". These words are named "graves"
Words that end in "ps", like "fórceps" and "bíceps".
Words which stress two syllables before the last one need an accent on it regardless of the last letter. These words are named "esdrújulas".
Words with stress three syllables before the last need an accent on it regardless of the last letter. These words are named "sobresdrújulas".