if your y value is increasing as your x value is increasing, the function is increasing.

for example f(x) = x

if x = 0, y = 0

if x = 1, y = 1

So as you go from left to right, your y value gets higher, thus it is increasing.

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I've attached some graphs of increasing functions.

(I feel like a kid with candy)

edit: Note that is not increasing at the point (0,0), but it is increasing everywhere else.