Your circuit is very easy to understand if you read the LM339 datasheet.
https://www.ti.com/lit/ds/symlink/lm239.pdf?HQS=dis-mous-null-mousermode-dsf-pf-null-wwe&ts=1671568309756&ref_url=https%253A%252F%252Fwww.mouser.mx%252FThe LM339 is four, independent Voltage comparators in a single package. That's all it is. So, using the one labeled #1 in your schematic, here is how that one works.
The #1 comparator has inputs on pins 4 and 5 and the output on pin 2. The outputs of the four comparators have an "open collector" configuration which means that there is an internal transistor with it's emitter connected to Gnd and the emitter goes to the output pin with no internal connections. This means that, in order to function, that transistor must have an external load resistor. That is R260, 100K in your schematic. That resistor tries to pull the output pin, #2 high and the comparator's internal circuitry can pull it low. This allows the IC to operate with one power supply while the circuit connected to the output can have another. For instance, the IC may have a 12 Volt supply while the load circuit may operate on 24 VDC.
The inputs for the 1 comparator should have Voltages between Gnd and Vcc (0 - 5 V in your schematic). Pin 4 is the inverting input and pin 5 is the non-inverting input. If the Voltage on pin 5 is higher than that on pin 4 then the open collector transistor in the IC is not turned on and the output is raised high by R260. And if the Voltage on pin 5 is lower than that on pin 4 then the open collector transistor in the IC is turned on and the output is driven low by that transistor.
Output 1, pin 2 has two additional components attached to it. They do not have much effect on the output logic. They are apparently there to protect the load (Zener diode, D23) and perhaps to filter the output or shape the rising and falling edges (capacitor, C36). I would need to see the circuit this output is attached to in order to explain them better than this.
The inputs to pins 4 and 5 are:
Pin 4 comes from a Voltage divider made of R258 and R259. They are connected between VREFV0 and Ground. The schematic does not tell us what VREFV0 is so the best I can say is the Voltage on pin 4 (Vpin4) will be:
Vpin4 = VREFV0 x 43,000/(43,000 + 100,000)
It appears that VREFV0 is a fixed reference Voltage created in some other part of the circuit. So Vpin4 should also be a fixed Voltage. But I could be wrong in this.
Pin 5 is connected to VCC1V0.
So Out1 on pin 2 will be:
High or VCC5V0 if VCC1V0 > Vpin4
and
low or Ground if VCC1V0 < Vpin4
That explains how the first comparator operates using the information available in your schematic. The other three comparators operate in a like manner but take their reference and checked Voltages from different places. It is not difficult so I leave it to the reader to work out the logic tables for them.
Comparator 2 uses the same reference (from R258 and R259) as comparator 1. This does not mean that they have any relationship other than that common reference. Nothing flows between the two input pins: 4 and 6. Both just have the same reference Voltage.
On the output side, Outputs 2 and 4 are connected and they share the same load resistor, R261. Since the two open collector transistors share the same load resistor, either one can pull the output line low. This is called a wired OR circuit. If Out2 OR Out4 is low, then the output line is LOW. Both must be high for the output line to be high. This output line has the same output protection/modification as Out1: D24 and C368.
Pin 7, In 2+ has a more complicated input circuit (R263, R265, and R269 all precision resistors). Each of these resistors comes from different Voltages from other parts of the circuit so I can not explain their interaction. Only that it is the combined Voltage that goes to pin 7 that matters. The line PG-DDR, which is connected to pin 7, goes to or comes from somewhere else. Again, without information about that connection, nothing further can be said.