From the
verb estar (always use the accent on the last
a):
(Usted/el/ella) está.
You/he/she/it is here.
(Tú) estás.
You are here.
The
demonstrative pronoun when modifying a noun never takes an accent:
Esta carta me partió el alma.
This letter broke my heart.
Estas personas vienen por primera vez.
These people are here for the first time.
The
demonstrative pronoun when used as a noun takes an accent on the first
e.
Ésta es la carta que me partió el alma.
This one is the letter that broke my heart.