Can you explain the photoelectric effect?

The photoelectric effect is one of the first pieces of experimental evidence of quantum mechanical phenomena. It describes how a material absorbs light and result in emission of electrons. Using a classical wave (as opposed to quantum) description of this process we would expect to see the kinetic energy of the emitted electrons to change with the intensity of incident light, however this is not what was observed in experiment where even very low intensities resulted in electron emission. Eisenstein posited that instead of the classical wave description of light, we use a quantum description where light is bundled into little packets (quanta) of energy which we call photons, with this and the idea that there is a threshold energy which must be exceeded for an electron emission to occur we understand the photoelectric effect through the following equation: K=hf-phi, where K=kinetic energy of electron, f=frequency of incident photon and phi= threshold energy.