Everyone basically knows how to use a seven segment display. Either the anodes or the cathodes are connected together and the others are each connected to a pin on the microcontroller. With a Arduino nano this looks as follows.
Via multiplexing and half an hour of soldering practice you’ll get something along the lines of this:
and since multiplexing is fun, here’s the button matrix that goes with the 7 segment output board:
Both boards are driven with SN74HC595 shift registers and some BC547 NPN-transistors for the ground switching. Nice little shenanigans to play around with arduinos.