explain why the skater must be at a specific height at the start to successfully reach the end of the ramp.
be sure to use the terms "potential energy" and "kinetic energy" in your answer.

Basically, because the skater will never use some kind of a boost, they will rely purely on forces. At the top of a slope, their kinetic E is zero, and their Potential E is as high as it will be.

The skater will not be able to ever get higher that the initial height without some kind of force helping it.