|If you are talking about Cat5/6 network cable then the only difference is the way the plugs are wired.|
The following diagram will explain.
There are two standards. EIA/TIA 568A and EIA/TIA 568B
It doesn't matter which one you use providing you use the same standard at both ends of the cable for a normal strait through cable. For a crossover cable one end is wired as 568A and the other as 568B.
The purpose of a crossover cable is to connect two similar pieces of equipment like two NIC to connect two computer directly or two switches if they don't have an uplink port. A crossover cable does the same job as a null modem cable when connecting two RS232 serial ports together.