h(x)=cf(x), where c>1, and "c" is multiplied with each of the y-coordinates.
(x,y) -> (x, cy) multiply y-coordinate by c
In this diagram, the parent function is f(x)=x² (blue)
It is then multiplied by "c," which is 2.
2 is greater than 1, so it is a vertical stretch. The resulting function is g(x)=2x² (red)