ESTAR VS. SER


Use of 'Estar':
  
To tell location.
	El libro est en la mesa.  (The book is on the table.)

To describe health.
	Estoy muy bien.  (I am very well.)

With adjectives to describe conditions.
	 Estoy muy ocupado.  (I am very worried.)

In a number of fixed expressions.
	Estoy de acuerdo.   (I agree.)
	Est bien.  (It's good./It's okay.)

To form present participle.
	Estoy estudiando ahora mismo.  (I am studying right now.)

  

Use of 'Ser': 
  
To identify people and things.
	Yo soy estudiante. (I am a student.)
	Esto es un libro.  (This is a book.)
	Alicia y yo somos amigos.  (Alicia and I are friends.)

To express nationality; with 'de' to express origin.
	Son cubanos.  (They are Cubans.)
	Son de la Habana. (They are from Havana.)
	De donde es Ud?  (Where are you from?)

With 'de' to express of what material is something made.
	Este bolgrafo es de plstico  (The pen is made of plastic.)

With 'para' to tell for whom or what is something intended.
	Es para la clase de ingls.  (It's for the English class.)
	Es regalo para Sara.  (It's a gift for Sara.)

To tell time.
	Son las once.  (It's 11 o'clock.)
	Es la una y media.  (It's 1:30.)

With de to express possesion.
	Es de Carlota.  (It's Carlota's.)

With adjectives to describe basic, inherent qualities or characteristics of people and things.
	Soy sentimental.  (I am sentimental.)
	El coche es muy viejo.  (The car is very old.)

To express generalizations (only with es).
	Es importante estudiar, pero no es necesario estudiar todos los das.  (It's important to study, but it is not necessary to study everyday.)


The main difference is that estar refers to temporary attributes while ser to permanent or more lasting ones.