When do I use 'ser' or 'estar'?

Both 'SER' and 'ESTAR' translate as 'to be', but they have different meanings.
SER is used to describe states of permanance: Descriptions, Occupations, Characteristics, Time, Origin, and Relationships.
You can remember this with the acronym 'DOCTOR'.
Examples: Yo soy Flora. I am FloraElla es inglesa. Ella is EnglishSimon es alto. Simon is tall.Hoy es miércoles. Today is Wednesday.
ESTAR is used to describe temporary states and locations: Position, Location, Action, Conditions (temporary), Emotions
You can remember these with the acronyms 'PoLo' and 'ACE'
Examples: Mi padre está arriba. Mi father is above.
Estamos en el café. We are in the café
Estoy lavando los platos. I am doing the dishes.
Esta triste. He is sad.