My real world function is about time and destination.
A function is a relation where each value in the domain has exactly one value in the range.
A relation is a set of ordered pairs (x,y).
The independent variable(x) of my function is the time.
The dependent variable(y) is the destination.
The domain is [7:00, 7:15, 7:28, 7:45].
The range is [Burger King, Safeway, Lucky's, Applebee's].
The graph on the left is a function because it passed the vertical line test. All values of x has exactly one value of y. The graph on the right is a relation because it failed the vertical line test. The x-value cannot have two outputs of y.