Is there a difference between the potential energy of an oscillator and the potential energy of the spring which is associated with? When we compress a spring horizontally without any object associated with it starts to expand? Is the potential energy convert into kinetic energy of the spring?
Entry level physics doesn't really think about where the energy is in the spring ( but it is in the molecule bonds that are being stressed). You just need to assume that you apply energy from somewhere ( like your muscles) and this energy is now in the compressed spring as potential energy. So you converted chemical energy (in your muscle) to potential energy. If the spring is released against a mass,, the mass will have all the energy as kinetic energy, and if the mass slides on a rough surface and stops it all becomes heat in the mass and surface due to friction.