In this learning track, we will first learn how to set up and run an Ansys Lumerical varFDTD simulation of a double bus ring resonator, collect the results and discuss how the results compare to 3D FDTD simulation results. We will then discuss the effective index method used by the Ansys Lumerical varFDTD solver to collapse a 3D geometry into a 2D simulation and highlight some of the differences between varFDTD and a traditional FDTD simulation. Following this, we will discuss the solver region, materials, sources and monitors used in varFDTD. Finally, we will show several example devices and results that can be obtained from the varFDTD solver.