I’m not really even going to try to explain how this works. Because I will muck it all up and make it confusing. I will, however, say that the Double Slit Experiment has ties to both Heisenberg’s Uncertainty Principle and Schrodinger’s Cat. It posits that electrons are, depending on whether or not they are being observed, either a wave (Schrodinger) or a particle (Heisenberg). Observed, the electrons pass through one of the two slits, behaving exactly as particles. Unobserved, the electrons pass through one or both or neither, behaving as waves.
A really great video can be found here.