What is the difference between ser and estar?

English only has one verb 'to be', but Spanish has two: 'ser' and 'estar'. This can be confusing, but it is important to know the difference as they have different uses and can change the meaning of the word that follows them.
In general, 'ser' is used to describe quite permanent things like your appearance, personality or nationality e.g soy inglesa, soy alta, soy simpática, but 'estar' is used with temporary actions happening in the moment or temporary emotions e.g estoy feliz.
There are some exceptions, like the fact that permanent location uses 'estar' for example describing where places are in a town, and when stating the time you use 'ser' which may seem temporary.
Therefore two key acronyms can help you to remember when each is used:
Estar is used for PLACE: Position, Location, Action, Condition, Emotion. e.g estoy sentada en la silla, la mesa está en la cocina, estoy comiendo, estoy enferma, estoy feliz.
Ser is used for DOCTOR: Date, Occupation, Characteristic (physical or personality), Time, Origin, Relatione.g hoy es el 1 de enero, Javier es médico, yo soy simpática, son las 4, soy de Inglaterra, Juan es mi hermano.