Ser or Estar?
Ser is used to refer to identity, like: nationality, gender, profession and origin. Below some examples:
Furthermore ser is used for expressions of time, dates, days and events. Below some examples:
Son las doce del mediodía.
It's twelve o'clock in the afternoon.
La semana pasada fue el cumpleaños de mi hermana Alexandra.
Last week was the birthday of my sister Alexandra.
Read more about expressing time and dates in the article about time in Spanish.
Ser is also used to tell what things are made of. For example:
La mesa es de madera.
The table is made of wood.
Los neumáticos son de goma.
The tires are made of rubber.
Also ser is used to indicate property. For example:
Estar is used to express the location of somebody or something, for example:
Estamos en la isla de Tenerife.
We are on the island Tenerife.
Los libros están sobre la mesa.
The books are on the table.
Mañana estaré en casa.
Tomorrow I'll be at home.
In addition estar is used for the expression of feeling, mood, emotion, physical codition or appearance. It's importante to notice that it's always a state of being. For example:
Carmen está resfriada.
Carmen has a cold.
La chica está bonita.
The girl looks pretty.
Furthermore estar is used for civil state, like: divorces, married, died, etc. For instance:
Also estar is used for things that are going on. In this case estar is use as auxiliary verb with the gerund -ing form. See the example below:
Read more about the use of the gerund in the article about the use of modes and tenses in Spanish.
Ser versus estar
Some other examples with clear differences between ser and estar:
El profesor es aburrido.
The teacher is boring.
El alumno está aburrido.
The pupil is bored.
Ella es bonita.
She is pretty.
Ella está bonita.
She looks pretty.
Concluding and summarising all this ser is more related to identity, estar is more related to a state or location.