Easing functions serve to animatechange a value during a time period, from a start valuestarting number to an end valuenumber.
You use that value to animate a property value of an element you want to animateobject in your game, such as position, rotation, scale, changing colors and other properties that use a value.
The different easing functions determine the "feel" of the animation, or how the value changes over time.
On the website you posted, the graph shows the value changing over time from a start to an end, so it doesn't mean the object you are animating will follow the path of the ball in the graph.