ok the "ya" in "see ya" is just short for the "you" in "see you" so they are just the same thing. and the phrases "see ya" or "see you" are both just slang for "see you later"
"see ya" is pronounced:
see is pronounced: c (like, when you say A, B, C)
and ya is pronounced like, "ya" with an "a" as in the "u" in unbelievable