A common question about origin is:
¿De dónde eres?
     Where are you from?

We answer with the verb ser which means to be.

The verb ser has different uses; one of them is to talk about origin or nationality, we add de after the verb.
In this context de means from.

Yo soy de México.
     I am from Mexico.
    Tú eres de Kentucky.
     You are from Kentucky.
Él es de Cuba.
     He is from Cuba.
El maestro es de la ciudad.
     The teacher is from the city.
Nosotros somos de Alemania.
     We are from Germany.
Los jóvenes son de México.
     The young guys are from Mexico.
Yo soy de Puerto Rico.
     I am from Puerto Rico.