Feb 10 - When is the word "to" translated as "que"?

I'm aware that "I have to go" is translated as "Tengo que irme" or "Me tengo que ir."

I think I've seen "I have something to tell you" translated as "Tengo algo que decirte"; is this correct?

And is the phrase, "I'm going to run to find something to eat" translated as either:

"Voy a correr a encontrar algo a comer",

"Voy a correr para encontrar algo a comer",

or "Voy a correr para encontrar algo para comer",

or should I use "que" instead of one of the "a"s?

Please help! Basically what I'm asking is how do I know when to use "que" or "a" instead of "to".