[LadyMoonlight]

The way I learned "ya" is pretty much what MMM said. It's "and" but not exclusive to just the things mentioned.

For instance (to use the previous ex.) : I'm buying milk and eggs and ham at the store. Use "ya"

I'm buying milk and eggs at the store. (If only buying those 2 things, use "to")

There's milk and eggs in the refrigerator. (I believe that using "ya" here is correct unless your fridge only contains milk and eggs.) Really this statement is "There's milk and eggs (and other things) in the fridge."

I hope this makes more sense (though I'm mostly reiterating using a different example)

LM