Cross over cables are used when you want to connect layer 3 kit (routers,switches etc) to one another. Everything else will use the standard 'straight through' cable. Easy way to identify the different types of cable is to hold the ends together facing the same way up (with the metal connectors facing upwards). If all the wire colours are in the same order it's a 'straight' if there not it's a 'cross over'. Simple innit...!
