Subject: What is the layperson's way to figure out circuit math?

I am working on creating a game in which players build a circuit, but there 
is a gap in my understanding of all of the math. It is difficult to find 
this "formula" because there are so many measuring systems. Let's say the 
interaction is that the players of my game place the virtual batteries and 
use resistors in the circuit to dampen the  current. For example, how do 
current and voltage both convert to watts? To illustrate, let's say I 
wanted to deliver 30 watts of elect.to light a lamp. Let's say the current 
coming from some batteries is shown to be 40 amps. Each resistor (say we 
use two) resists 5 volts. Is this correct? 

Re: What is the layperson's way to figure out circuit math?