Yo is also
Spanish for I.
"Yo no tengo ganas de salir."
I don't feel like going out.
Since Spanish verbs are conjugated very precisely, one need not use the personal pronouns at all. They're mostly used when you want to specify exactly who is doing something.
Quiero Taco Bell.
Quien quiere Taco Bell?
Yo quiero Taco Bell.
I want Taco Bell.
Who wants Taco Bell?
I want Taco Bell.