I'm having troubles to manage and understand how to do to get acceleration and deceleration with a shape following a path using the speed graph.

I understand what a curve means when it's going up or down.

This is my first attempt but applied to lettering

https://goo.gl/HwDYP6
I think a 2d roller coaster is the best exercise to learn the use of speed variations. So I drew a path simulating a 2d roller coaster with the whole possibilities that a roller coaster could have without rotations (just hills, loopings downs... )

If I just try a loop part isolated, is easy to get the right speed at the beginning, in the middle and at the end of the path. BUT if I try to make the speed modification having the whole roller coaster circuit together, I'm not able to adjust a correct speed variation for each stage.

I hope this message has sense. Thanks

Chris(tian)