Explain this in a simpler and more understandable way:
Replace all variables with numbers so that all conditions are satisfied  by turning green and showing equivalence signs ≡ . In mathematics the notation A ≡ B mod N says that A and B differ only by a  multiple of N, in other words, they leave the same remainder when being divided by N. At least 2 different colours need to be used. For example, 1,4,7 represent   the same colour mod 3 because all leave the remainder 1 in a division through 3. 