How is "ya" used in Spanish?
This little word is very complicated and depending on context has different meanings. Here are a few,
Ya - Already
Ya - Now
Ya - Right now
Ya - Later
Ya - No longer
Ya - Also used for emphasis, ex, Ya lo sé - I already know
No ya - Not only
Ya que - Now that
Ya que - Since
One other use I've heard is when it means "that's it," or "there you have it," or "you're done/set."
For example, "Le pagas quince dólares al hombre en efectivo, y ya" would be "You pay the guy fifteen dollars in cash, and that's it/there you have it/you're done/set."
I'm pretty sure this is just shorthand for "ya estás (or any conjugated form of "estar"), which roughly translates to "there you go/you're set."
One more example, "¿Quieren más pan"? "No gracias, ya estamos". Do you want more bread? No thanks, we're set.