The 7-segment display is familiar from the good old digital clock. We have a few different colors (at least yellow and blue), with common cathode. So it is basically 8 leds (7 in the segment + the dot). The hard way to use it is to connect each one to arduino digital pins, and then define which pins are on and which are off to draw numbers (or some letters – try writing M or K)
Here is a good tutorial for Basic Arduino connection.
The more complex way is to use a microcontroller to control the leds. Instructables has a tutorial about the basics of this method.