This is a fantastic piece of simulation software from PhET which allows you to build electric circuits and study what happens when you change resistance or voltage.
Download the simulation by clicking on the picture.
To get you started why don`t you build this circuit
- How the current in the circuit changes when the 8 ohm resistor is doubled
- How the voltage will change across the 24 ohm resistor when the 8 ohm resistor is doubled.
Have some fun building more circuits and investigating the the current, voltage and resistance of the circuit.