The chip requires a dual voltage power source. Check your motherboard manufacturer for suitability. Its purpose is to provide a time base to coordinate the various components on the motherboard. It is very much like the instruments of an orchestra following the conductor's timing. Other microprocessor manufacturers may use other frequencies.
Higher frequencies are potentially better.
Intel may, someday soon, add 100 megahertz to the Pentium II series. Actually, this is the internal clock frequency established by a programmable clock generator. Bus clock frequency is also an important factor in overall system performance. Again, the ones most commonly found are the same frequencies as the microprocessor's external clock. Non-Intel 586 and 686 class microprocessors may have radically different bus speeds.