What is the purpose of a comparator?

The main purpose of a comparator is the conversion of ADC(analog to digital conversion). In its input two supply voltages are applied and their differnce determines either a high or low signal of digital signal like to make which bit is high and which is low in the form of V++ and V--. If the diffrence between the two voltages is greater means positive the output will be V++ and if lower means negative the output is V--.