Ser or Estar

In Spanish there are two verbs that mean “to be” something. Because there are two different verbs meaning the same thing, there are of course different reasons to use each verb.  In general, you would use the verb ser to describe things that are permanent, and estar for things that are temporary.  For example, we say Yo soy alto,  “I am tall”, because that is permanent; I’m always tall. And we say Yo estoy triste, “I am sad,” because that is temporary; hopefully tomorrow I won’t be sad anymore. My mood can change.

Ser To Be Estar
yo soy I am yo estoy
tú eres You are tú estás
él, ella, usted es He/She is él, ella está
nosotros somos We are nosotros estamos
vosotros sois They are vosotros estáis
ellos, ellas, ustedes son You are ellos, ellas están

Use of the verb “SER“
To identify the subject; tell what it is
Ella es ingeniera. She is an engineer.
Ese animal es vaca. This animal is a cow.
To show origin
¿De dónde eres? Where are you from?
Soy de Montville. I am from Montville.
To show what something is made of
La alfombra es de lana y las cortinas son de algodón. The carpet is made of wool, and the curtains are made of cotton.

Note: In this example the first thing, la alfombra, uses es because it’s singular. The second thing, las cortinas, uses son because it’s plural. 
To show possession/ownership
La mochila es de Miguel. It is Miguel’s backpack.
¿De quién es el estéreo? Whose stereo is it?
To show destination or recipient with para (for)
¿Para quién son las flores? Who are the flowers for?
Son para mi madre. They are for my mother.
To show time of day or another time expression
Es la una y media. It is one thirty.
Ya es tarde. It is already late.
To show when or where something takes place
El concierto es a las ocho. The concert is at eight.
La junta es en el auditorio. The meeting is in the auditorium.
With adjectives to describe qualities or characteristics that are permanent or basic to the individual or object described
Es una casa muy grande. It is a large house.
Las fresas son rojas. Strawberries are red.
El hielo es frío. Ice is cold.

Use of the verb “ESTAR“
To show location
Estamos en el consultorio. We are in the doctor’s office.
Fenway Park está en Boston. Fenway park is in Boston.
To show a state or condition (usually temporary) of a person or thing, usually resulting from a change
¿Estás enfermo?  No, estoy aburrido. Are you sick?  No, I am bored.
El dictator está muerto. The dictator is dead.

Note:  Although death is permanent, there was a change in the dictator’s condition (from alive to dead), so you would use está and not es.
With adjectives, to comment on a condition or state that is unexpected, causes surprise, or represents a change from the norm
¡Está grande tu casa! Your house is really big!

Note: You are not commenting about the fact that the house is large (which is a permanent thing), but that you are surprised that the house is so large.

Comparison of “Ser” and “Estar”
¿Cómo son tus padres? What are your parents like?
¿Cómo están tus padres? How are your parents?

In the first sentence you are asking about something that is permanent.  In the second sentence you are asking what condition they are in (are they sick, are they well?)
Es muy nervioso. He is very nervous ( a nervous person).
Está muy nervioso. He is very nervous (about something).
Es un profesor aburrido. He is a boring professor.
El estudiante está aburrido. The student is bored.

Some words change their meaning depending on whether they are used with ser or estar.
         
    With ser   With estar
aburrido   boring   bored
divertido   amusing   amused
enfermo   sickly   sick
triste   dull   sad
vivo   lively   alive