Wiring a 28 segment LED bargraph (to an Arduino)
This is a 7 shared cathodes, 4 shared anodes display. Pretty standard way to drive complex LED displays:

There's groups of LEDs that share one cathode connection (in this case, those are 7 groups of 4 LEDs each), but all have different anode connections (of these, there are 4 groups of 7 LEDs each). There's no two LEDs that light up at the same time if you just connect one anode and one cathode connection!

Therefore, you need 11 connections to connect this display, 4 of which need to be able to source the LED forward current (i.e. be pulled high), 7 able to sink that amount of current.

So, to light up a segment, you pull down the corresponding cathode connection and the up the anode connection.

You do that for every segment, one after the other, quickly enough: the human eye is way slower than a microcontroller, and thus, although you're not lighting up all segments at once, it looks like you do.