Work is the amount of energy transferred into or out of a system by a force exerted on that system over a distance. The work done by a conservative force is path-independent and zero over any closed loop — potential energies are associated only with conservative forces. The work done by a nonconservative force (most commonly friction or air resistance) is path-dependent.
A box slides down a frictionless curved ramp from a height h to the ground. (a) Does the normal force do work on the box? (b) Is gravity, which does do work here, a conservative or nonconservative force? (c) Would the work done by gravity change if the ramp had a different shape but the same start and end heights?
Try it on paper first, then reveal each step to check your work.