7-Segment Drivers: How do they work/how to handle them?
Look at the functional diagram of the datasheet you posted.

Each digit of the display has eight LEDs, with either all of their cathodes or all of their anodes tied together (the driver will say whether it's common cathode or common anode).  Each segment of each digit has their other side tied together.  This lets the driver turn on each digit in turn, to show the desired pattern on the segments.

The communications to the driver uses synchronous serial.  You shift in bits using the DIN and CLK.  Google "SPI" for how that works if it's not familiar to you.

Those bits are completely ignored by the rest of the device until you drive *LOAD low.  At that point the bit pattern is interpreted as eight bits to write and an address -- those eight bits go into the 8x8 dual-port RAM (and it looks like you can do some setup, too).

There's a lot of stuff going on inside that part.  Expect to do some close studying of the data sheet before you get it all figured out.