You shine light of just the right wavelength (shorter wavelength = higher energy) at a metal and this causes the displacement of electrons = current.
so this kinda makes sense to me but still
A metal can be thought of as a lattice of atoms with their inner shell electrons bound in place, but their outer shell electrons or valence shell electrons are pretty much free to move throughout the lattice.
When light of the right wavelength transfers it’s energy to an inner shell electron it becomes excited and jumps away from the atom; this causes a current as now there’s a positively charged ‘hole’ where another electron will have to jump in to take it’s place. Current flows more easily through a metal because the activation energy is being overcome by the energy provided by the light.
If you were trying to figure out how the photoelectric effect explains that light has wave characteristics it’s down to the fact that if light was behaving as a particle and not a wave then by increasing the amount of photons this should overcome the threshold energy for the photoelectric effect to occur. However, this was not observed as only decreasing the wavelength does this. (See below: Zinc becomes more conductive under UV light)
Hence it must be a wave in this case because wavelength is important and momentum of a proton changes as a function of wavelength. There’s an excellent description of that here.