What is the difference between ser and estar and when should I use them?

Both are translated as 'to be', but ser is generally used for permanent qualities, whereas estar is normally used for temporary conditions or states- this is ideal to use as a general rule of thumb. However, there are some specific uses which will make it easier to choose the correct one to use if you learn them. Ser is used for people's names (e.g. Soy Maisie), nationalities, professions, physical descriptions (e.g. Soy bastante baja), possession, material/what something is made from, time (days, months, time of day), events (e.g. la clase es en ese edificio), evaluations (e.g. es evidente que es verdad) and the passive voice.Estar is used for location, temporary occupations (e.g. Ahora estoy de secretaria pero soy arquitecta), emotional state (e.g. Estoy feliz), physical state (Está bastante delgada), an action in progress using the gerund (e.g. Estoy estudiando) and it can be used with the past participle (La puerta está cerrada).