A conservative force is a force that stores energy. Examples of conservative forces include the spring force, the gravitational force, and the electric force. In physics there are also non-conservative forces that do not store energy.
Conservative forces store energy in the form of mechanical energy. Potential and kinetic energy are the two forms of mechanical energy that are conserved. Potential energy is at its maximum when particles are at their maximum height, and kinetic energy is at its maximum when particles are at a height of zero. As particles move and conserve energy under the influence of conservative forces, potential energy is converted into kinetic energy, or vice versa, to conserve the overall amount of mechanical energy.