There are two letters in Spanish that vary when combined with the vowels. The letter c when accompanied by the vowels "a, o, u" is pronounced as "k". When it is accompanied by the vowels "e, i" it is pronounced as an "s". The letter g when accompanied by "a, o, u" is pronounced as in the word "go". When accompanied by "e, i" it is pronounced as the letter "h" in "hero".

c
Yo estoy casado.
     I am married.
Yo necesito descansar.
     I need to rest.
No tengo licencia.
     I don't have a license.
Trabajo con los caballos.
     I work with the horses.
Tú corres a la escuela.
     You run to school.
g
El gato es gordo, blanco y negro.
     The cat is fat, white and black.
Soy vegetariano.
     I am a vegetarian.
Nosotros jugamos en el gimnasio.
     We played in the gym.
Jugo de mango.
     Mango juice.
Me gusta el verano.
     I like the summer.