The trouble with electricity is that you can't see electrons flowing through the circuit. It's not very intuitive. We tend to describe electrical laws and characteristics using analogies to the things that we can see in the world around us. Here's my favorite character, the BitMonkey demonstrating Ohms law (pdf | png) by blowing through a straw.

Useful formulas and rules (pdf | png)

Symbols for most common components (pdf | png)

Wiring diagram of Serial Com setup (pdf | png)

Hyperterminal Settings (pdf| png)