Here is one of my first little project I did with my Arduino Uno.
It's is just a little light seeker. The servo turns towards the light.
I made a video to show you what it does :
Step 1: The wiring
The only difference is that I fixed the photoresistors on the servo (but I couldn't do it with the program)
Also I used a 9V battery in the video, it was plugged in Vin and GND.
The resistors are 200 Ohm for the LED's and 10 KOhm for the photoresistors.