When do we use the verb ser and when do we use the verb estar?

In Spanish there are two different verbs for the verb "to be" in English, Ser and Estar. The two are not interchangeable, as they have two different uses. We use the verb ser when we are describing something permanent. i.e. nationality "soy inglesa" or a characteristic of a person for example "su pelo es rubia". In contrast we use the verb Estar when talking about something temporary i.e. location or mood "estoy cansada" "estoy en mi dormitorio".