E nergy is the ability to do work and work changes the energy of objects. Work requires the application of force over a distance to achieve that change in energy.
A book on the floor has zero potential energy. When I pick it up and put it on the table, I do work on the book because I gave it more potential energy. Work = change in energy. That is why both work and energy are measured in Joules. To do the work I applied a force (equal to the weight of the book) to the book from the floor to the tabletop. Work equals the force times the distance, in units of Newtons times Meters. Therefore 1 Newton-Meter (NM) equals 1 Joule