Kinetic energy is energy in the actual motion of an object.
Potential energy is energy stored as a result of the position (e.g. height) of an object.
When a pendulum swings, it's ptoential energy is maximum when the weighted end is raised to its greatest height, and the pendulum is momentarily stationary so that its kinetic energy is zero.
As the weighted end falls under the influence of gravity, the potential energy is converted into kinetic energy. The pendulum has minimum potential energy when it is aligned vertically, with its weighted end at the lowest point. At that moment it has maximum speed and maximum kinetic energy.
As the pendulum continues to swing, energy "oscillates" sinusoidally between kinetic and potential energy. Both kinetic energy and potential energy are measured in Joules (J) in the SI system of units.
Best wishes - Majikthise.
You can read about potential energy here - http://funadvice.com/r/163dvcpgqrc