No worries we all were once.
Basically the colour output of the brick texture gives each brick a value from 0-1 the “greater than” nodes (math node) are asking “is the value of this brick greater than my value?”
The result gives you a black and white mask (yes=1 or no=0) that you can use as a factor to assign the colours.
You could replace the “greater than” nodes with colour ramps set to “constant” and 2 stops (black and white).
The UV mapping of images in the brick texture node cover the whole area (individual bricks are not taken into account.)
I am not sure what your problem is but there are alternative “brick node” setups that give you a uv map per brick.
Lazy dodo’s “Brick tricks” addon gives you a uv map per brick if that helps you.