To show possession        El libro es de Miguel The book is Miguel´s

To show origin El es de Cuba He is from Cuba

To show what material something is ,made of La falda es de seda The skirt is (made of) silk

To describe a person, place or thing (characteristic, size, length, religion, color, personality, profession, etc.). This description is something that does not change at all in some cases. Ex. She is american. In other cases, the change is gradual and slow. Ex. Ana is young. She obviously won´t be young forever but, since the change is gradual, we use the verb SER

Juan es inteligente	Juan is intelligent	characteristic
Madrid es grande	Madrid is big	size
El cuento es largo	The story is long	length
Ella es católica	She is catholic	religion
El coche es rojo	The car is red	color
El es muy serio	He is very serious	personality
Ellos son médicos	They are doctors	professions

To express time, dates, days of the  week. Son las cinco It is 5:00 Es el cuarto de julio It´s the fourth of July Es lunes It is Monday