What's the difference between "estar" and "ser"? (Both of them mean "to be")

“Ser” is used to describe permanent or long lasting qualities. It is also used to talk about date and time.Hoy es lunes, son las 12.30 = Today is Monday, it’s 12.20Examples:Laura es alta = Laura is tall (this is an inherent characteristic to Laura, she is always tall)Yo soy cocinera = I am a cook (long lasting state)“Estar” is used to talk about states that can change or are temporary. It is also used to describe temporary locations and ongoing situations.Example:Hoy estoy muy triste = Today I’m very sad (temporary mood)Estoy en la biblioteca = I’m at the library (temporary location)Estoy cocinando = I am cooking (ongoing situation)Be careful!In some sentences you can use "estar" and "ser" but the meaning will change:Ella es graciosa = Se is funny (She is always funny, it is part of her personality)Ella está graciosa = She is funny (She is not usually funny but at that specific moment she is behaving funnily)