First, what is Ohm's Law? Wikipedia has this to say, Ohm's law states that the current through a conductor between two points is directly proportional to the potential difference or voltage across the two points, and inversely proportional to the resistance between them.
Now, personally I never really learned what it says I just learned how to use the chart above. When trying to solve for an unknown in the circuit and you have at least 2 knowns you can go to your chart, look at what you are trying to solve and use the formula that matches your two knowns.
For example: say I know that my resistance of the circuit is 100 ohms and the voltage in my circuit is 12 volts, going to the chart and looking in the beige shaded green shaded area since I am looking to find current(amps) I see that the formula that uses both ohms(R) and voltage (V) is I=V/R or Voltage divided by the resistance gives you current.
For now get a feel for what this chart looks like and how to use it. I will go into more detail about what ohms, voltage, current, and power mean at a later time.
If you'd like to try some sample problems to get familiar with the chart try out these.
I when V= 12volts and R=120 Ohms
R when I=2amps and V=6 volts
V when R=200 Ohms and I=6 amps.
Feel free to put the answers in the comments section and e-mail me if you have any questions.