The green color indicates positive voltage, and the gray color indicates ground (or earth). The movement of yellow dots indicates current (in the conventional direction). The left side of the circuit shows a voltage source providing 5 volts, and the current flows through a number of switches and resistors to the right. The amount of resistance in ohms is shown to the right of each resistor.
To turn a switch on or off, just click on it. If you move the mouse over any component of the circuit, you will see a short description of that component and its current state in the lower right corner of the window.
If there is only one switch closed on top and one closed on the bottom, then there is a single path through the circuit, and by Ohm's Law, the current will be equal to 5V divided by the total resistance through the current path.
There are four colored stripes painted the body of the resistor, they are grouped closer to one end that to the other. For someone who already familiar with color code, this stripes are enough to identify this as 47 ohm, 5% resistor.