Unfortunately there is no layman's version of arc flash calcs.
If you understand what an arc flash is (essentially a fault that uses the air as a conduction path resulting in heat, molten metal, light, sound, shrapnel, etc), then the calc tell us how much energy is may occur during one of them. With that incident energy, we can pick proper protective equipment.
Are you looking for actual formula? Have you reviewed NFPA 70E?