What is the difference between Ser and Estar?

Both these verbs mean "to be" in Spanish, whereas in English we only have one. This can make it confusing, but there is a general rule you can use to remember which you have to use. "Ser" is used for things which are permanent and usually unchangeable. For example: nationality (soy inglesa), physical appearences (es alto), characteristics (eres inteligente). "Estar" is used to describe a state, something which can change, and also to describe something. For example: temporary feelings (estoy cansada), location (está en Espana), description (estaba oscuro).