What is the difference between 'ser' and 'estar'?

Although they both translate to 'to be' in English, in Spanish we use these two different verbs, and it depends on the quality you are trying to describe. For example, 'estar' is used to describe something temporary. "To be tired" becomes "Estar cansado", because you won't be tired at all times. Imagine 'estar' as having an expiration date. If there is an action you can do that will change what you are describing, you use 'estar' Examples of times you use 'estar' are: emotions -such as happy or sad, physical states -such as hungry or tired. On the other hand we have 'ser' which is used to describe something that doesn't really change. "I am Teresa" for example, becomes "Soy Teresa", because I don't stop being Teresa. Ser is used for things such as names, nationalities, or personality traits.