Based on my math teacher ,"FUNCTION" is a special type of relative such that no two ordered pairs of the set have different second coordinate corresponding to the first coordinate.
While "RELATION" is a set of ordered pair of mathematical quantities.
Example of Function & Relations:
(4 , 8) x = 4
f(x) = 4x - 8
y = 4(4) - 8
=16 - 8
:)) , (ahm do i need to explain my example??)