Learn the basics using free online electronic circuits simulation, and different physics and chemistry laws used in the engineering.
Simulation
Founded in 2002 by Nobel Laureate Carl Wieman, the PhET Interactive Simulations project at the University of Colorado Boulder creates free interactive math and science simulations. PhET sims are based on extensive education research and engage students through an intuitive, game-like environment where students learn through exploration and discovery.
Click on the respective simulation to run the program online.
Very useful article.