What is the difference between the verbs "estar" and "ser"?

Both "estar" and "ser" mean "to be". However "estar" should be used when describing something temporary. For instance, when describing a location or explaining a state that an object is in (su madre está en el baño, las tiendas están abiertas). "Ser" is used for more permanent explanations e.g. occupation, nationality, time and date or possession (Mis padres son ingleses, Ana es inteligente, mañana es martes).