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

Mi esposa es doctora. - My wife is a doctor.

Ser is used to indicate an inherent characteristic or quality:

El niño es guapo. - The boy is handsome.

Ser is used to indicate origin:
Yo soy de Colombia. - I'm from Colombia.

Ser is used to express ownership or possession:
Ese carro, el cual está muy sucio, es de Enrique. - That car, that is very dirty, is Enrique's.

Ser is used to express the time of day:
Son las doce. - It's twelve o'clock.

Ser is used to talk about dates
Es el primero de enero. - It is the first of January.