Ser is used to signify equivalence or identity between two elements:

Alberto es doctor.
Alberto = doctor. Alberto is a doctor.

María es una buena persona.
María = buena persona. Maria is a good person.

Ramón es colombiano.
Ramón = colombiano. Ramon is Colombian.

Ser is used to indicate origin:

Diego es de Perú. Diego is from Peru.
Este tapete es de México. This rug is from Mexico.

Ser is used to express possession:

Esa bicicleta es de Gustavo. That bike is Gustavo's.
Las llaves son de Julio. Those keys are Julio's.

Ser is used to talk about time:

Son las dos. It's two.
Es la una y media. It's one thirty.

Ser is used to talk about dates

Hoy es el cuarto de junio. Today is the fourth of June.
Es jueves. It's Thursday.

Estar is used to signify the location of an object:

La escuela esta al lado del correo.
The school is next to the post office.

Estar is used to express the present progressive:

Estoy escribiendo. I am writing.
Juan está escuchando. Juan is listening.

Estar is used to indicate a resultant condition: estar + past participle

Estoy cansado. I am tired.
Estamos despiertos. We are awake.