Download the Adafruit LED Backpack library from github - This code provides support for the mini 8x8, 1.2" 8x8, 7-segment, bargraph, alphanumeric and bicolor LED matrix backpacks.
To download click the ZIP download button, rename the uncompressed folder Adafruit_LEDBackpack. Check that the Adafruit_LEDBackpack folder contains Adafruit_LEDBackpack.cpp and Adafruit_LEDBackpack.h Place the Adafruit_LEDBackpack library folder your arduinosketchfolder/libraries/ folder.
You may need to create the libraries subfolder if its your first library.
You'll also need to download the Adafruit GFX library - its not actually used for the 7-segment, its only for the matrix backpacks but its still required. Install just like the library above. Restart the IDE
- The backpacks all use the HT16K33 chip solely for LED driving - the mini 8x8's use the 24 pin version and the others use the 28 pin vesion