The verb 'ser' meaning to be, is used for permanent situations or statuses. e.g. Pablo es un chico aburrido = Pablo is a boring boy. 

The verb 'estar' also means to be but it is used for temporary situations or statuses. e.g. Estoy muy aburrida = I feel bored. e.g. Estoy muy cansada: no dormì nada esta noche.= 'I feel very tired: I did not sleep at all last night.'