When I was still in the University learning basic electronics and circuit designs, we have to do many calculations on paper. It is hard to imagine how the current flow in the reality. Nowadays, there is a good simulator online which is free and powerful, it is pretty promising to me. You can take a look here: http://www.falstad.com/circuit/
via http://www.scienceprog.com/free-fast-and-useful-java-based-circuit-simulator/
