clockdisplay is a library for seven-segment 4-digits displays, typically used in alarm clocks. This library is designed for use in Arduino projects.
There are a couple of examples, you can see them in your Arduino IDE, in File > Examples > clockdisplay.
This kind of displays usually have 16 pins to control all the segments:
They also have another pins for dots and some extra function, not deemed on this library.
Supported display models:
There is a PDF file in models folder showing the pinout, so you can find out which pin activates which segment with each cathode, for each model implemented in the library. It also shows how to add additional electronics needed for better performance.
If your display has a cathode (or anode) for each digit and a pin for each segment, then there is a more suitable library for you.