How many letters represent the k sound in spanish? and which ones?

There are 2 letters one of them is q and the second one is k. The letter k doesn’t apply all the time but most of the time it does. For example my name is in Spanish “Krystal”clearly it starts with a k. The latter q applies all the time like when you say que this means what.

1. hoy es el domingo ( sunday ) 2. mi cumpleaño es nueve de octubre ( oct 9 ) 3. yo no salgo por vacationed de navidad4. ¿comó estas?