How do you calculate POTENTIAL and KINETIC energy?

Potential Energy = mass x acceleration of gravity x height

Kinetic Energy = (1/2) mass x velocity x velocity

acceleration of gravity = 9.8 m/s^2

if friction is negligible (which i'm not saying it is) then the kinetic energy comes from the initial potential energy. so potential energy is mgh, and however much that decreases kinetic energy increases so

u=mgh

k=mg(h0-h)

where h0 is initial height and h is current height. but if friction is not negligible then you have to use 1/2mv^2 for kinetic energy. to determine if friction is negligible or not just let it go and see if friction slows it down a noticeable amount, or ask your teacher he might tell you to either neglect friction or not.