What do SER & ESTAR express?

SER → ESSENTIAL CHARACTERISTICS
ESTAR → SITUATIONS

SER introduces the essence of any given noun (people, places, animals, objects, concepts and ideas). The essence of a noun is any quality or attribute that expresses how someone or something is perceived. This is the underlying essence of SER.

• Amira es argentina.
  Amira is Argentinian.
  
• Brasil y Uruguay son países.
  Brasil and Uruguay are countries. 
• Los gatos son mascotas limpias.
  Cats are clean pets.
• Tu casa es grande. 
  Your house is big.

ESTAR expresses the situation of people, animals and objects, such as their state of being and location.

• Estoy cansado.
  I’m tired.
  
• Micaela está enferma hoy.
  Micaela is sick today.
  
• Estamos de vacaciones.
  We’re on vacation.
  
• Ana e Ignacio están trabajando.
  Ana and Ignacio are working.
  

SER expresses the location of activities and the concept of a destination. (Essential characteristic of the activity)

• La manifestación es en el centro.
  The demonstration is downtown.
  
• La clase de español es en el salón 103.
  Spanish class is (takes place) in room 103.
  
• —¿Es acá? —me preguntó el taxista.
  —No, es allá en la siguiente cuadra.
  “Is it here?”, the cab driver asked.
  “No, it’s over there on the next block.

ESTAR expresses the location of MATTER, such as and people, animals, objects, & places. (Situation of the person or object)

• Los manifestantes están en el centro.
  The protestors are downtown.
  
• Los estudiantes están en clase ahora.
  The students are in class now.
• El banco está en la siguiente cuadra.
  The bank is on the next block.

SER + PAST PARTICIPLE expresses actions in the passive voice. (Essential characteristic of the action)

• El cuento fue escrito por Borges.
  The story was written by Borges.

ESTAR + PAST PARTICIPLE expresses the resulting state of an action. (Situation of the person or thing after the action acted upon it)

• El cuento está traducido en varios idiomas.
  The story is translated in several languages.
  

ESTAR + GERUND (PRESENT PARTICIPLE) expresses an action in progress. (Ongoing situation)

• Los manifestantes están protestando la guerra.
  The demonstrators are protesting the war.