Normally, LED displays have only one "common cathode" or "common anode" per digit and seven segment connections, or perhaps eight, if one includes the decimal point, and even nine such connections if a colon is provided. That would mean seven segment connections and one digit connection for each digit. A digital clock would, presumably, have four individual digit-select connections, i.e. one for each digit.

Now, anything is possible, but I don't presently see a rational way of encoding four digits with three cathode (or GND) connections.

However, there are digit selectors, e.g. 7445, etc, as well as the drivers Erik mentioned, which take a BCD digit address as an input and provide a high-current-capable negative-going digit-select as an output corresponding to that address. If such a device is combined with a series resistor for each anode (segment) and a current source for each segment, e.g. 7446,7447,7448, or even CD4511, you can then produce a multiplexed display by simply timing the segment data and digit select correctly.

I'd be quite surprised if many approaches to this problem aren't available for your inspection via GOOGLE. Why not start with a search on 7-segment display. You might look at the 7-segment display and see whether you can find a part number. Searching for that might shed light on what each connection on the display module is supposed to be.

RE