(x, y) -> (a, f(a)) -> (domain, range) -> (input,output) -> (arguement, value)
EXAMPLE
Set:
A = {a1, a2, a3, a4}
B = {b1, b2, b3}
f = {(a1,b1), (a2,b2,), (a3,b1)}
Domain f: {a1, a2, a3}
Range f: {b1,b2}
Domain is your input into the function and the Range is your output.