An electrical double layer is an interface between a charged surface and a salt solution, and understanding its structure is crucial to explain numerous fundamental phenomena associated with electrokinetics and colloidal science and finds application in many membrane separation technologies. While the classical mean-field Poisson-Boltzmann (PB) theory for electrical double layers is physically intuitive and numerically solvable, it has limitations. Specifically, it is applicable only to monovalent salts, low surface charges, low salt concentrations, and uniform dielectric media. These limitations arise from the neglect of three crucial factors: spatial correlations between ions, variable dielectric media, and the finite-size effects of ions and solvent molecules. Incorporating these factors is essential to explain many important phenomena such as vapor-liquid coexistence in ionic fluids, reversal of ionic current in charged nanochannels, attraction between like-charged surfaces, and repulsion between oppositely charged surfaces. In this poster and I will demonstrate the application of a new theory entitled ``Modifield Gaussian Renormalized Fluctuation Theory" that addresses the limitations of mean-field Poisson-Boltzmann and successfully models the aforementioned phenomena.