If a word follows the stress rules, no written accent is required.  

Regular stress rules

Stress falls on the last syllable for words ending in a consonant (except -n or -s)

e.g. azul, jugar, hablador

Stress falls on the penultimate syllable for words ending in a vowel, -n and -s

e.g. la cama, el parque, el libro, un joven, los niños.


If a word is stressed in an irregular way, the position of the stress is shown by an acute accent on the stressed vowel.


Irregular stress

el árbol, el móvil

estúpido, compró, los jóvenes, la estación



Accents also differentiate between words which are otherwise spelt in the same way:


aquel libro, aquella pluma, ... that book, that pen aquél, aquélla, ... that one
aun even aún still, yet
de of present subjunctive of dar
el the él he, it
ese libro, esa pluma, ... that book, that pen ése, ésa, ... that one
este libro, esta pluma, ... this book, this pen éste, ésta, ... this one
mas but más more
mi my me (after prepositions)
se reflexive pronoun I know, tú imperative of ser
si if yes
solo alone sólo only
te you (object pronoun) tea
tu your you (2nd person singular)