How are potential and kinetic energy related to one another?

Potential energy is the energy that can be stored in a system when certain types of forces act between its components. Kinetic energy is the energy associated with the motion of an object. According to conservation of energy, the total energy of an isolated system remains constant , energy may change from one form to another form within a system. Loss in potential energy is converted into kinetic energy and vice versa. Example is roller coaster. At the top most point of the track, all the potential energy is stored in the cart. As the cart moves towards bottom most  point, potential energy converts into kinetic energy but the total energy of the system remains constant. i.e ( initial potential energy + initial kinetic energy = final potential energy + final kinetic energy). Hope this helps! 

Efficiency is an action of doing something. for example when you take a test. good efficiency means you did well but bad effeciency or no effiency means you did bad.