If you've been using the YwRobot power supply, it is time to remove it from the breadboard or at least turn it off. We'll be using the Arduino UNO module and it has its own power supply.

Note on Arduino Serial Driver: The Arduino UNO modules in HackerBox 0000 have the new CH340/CH341 serial driver chip instead of the traditional FTDI serial chip. A driver (available for OS X, Windows, and Linux) for the CH34x chip generally needs to be installed on your computer for the Arduino IDE to communicate to these boards. Here is a video on the topic.

To get warmed up on microcontrollers, here is a detailed but gentle introduction on how to control LEDs from an Arduino microcontroller module.

The schematic and photo here show how to wire up the RGB LED which is really three LEDs in one package with their anode terminals wired to a common anode on the longest pin (number 2). The attached Arduino code shows how to cycle through the many colors possible with the RGB LED.

As noted before, the more current pushed through an LED, the brighter it is. More current is achieved using a smaller current limiting resistor (verify this using Ohm's Law). An important consideration is that you can only suck so much current through the delicate silicon of a microcontroller. To avoid drawings too much current, we can use larger limiting resistors, but then the LEDs will not glow as brightly. A better solution is to use a transistor (such as one of your 2N222 transistors) as a switch. The switch can be controlled using a tiny amount of current from the microcontroller to switch a much larger amount of current through the LED. In this way, the transistor works a bit like a relay, which you may want to read about as well. Here is a tutorial on driving an LED with a transistor.

It is somewhat astray of DC circuits, but here is an example of using your photoresitors with the Arduino.