Click the play button on the emulator. It will scroll "255". If you click and hold leg 0, the emulator will start scrolling 0 instead. This shows us the highest and lowest value our analogue leg can read.

Load your program onto your CodeBug and shine a bright light on the LDR, the value scrolling will change to numbers within the 0-255 range. When the light is shone on LDR the value will be lower.