Straight-thru and cross-over Ethernet cables re used to connect the devices together on an Ethernet network. The Ethernet network is the wired network of computer devices that you see all the time. The Ethernet is using cable that has four small pairs of wires inside to connect the devices so they can talk to each other.
When you go to connect your PC to the modem/switch that connects the Internet to the world outside your business or house you usually use a straight-thru cable to connect the boxes together. There are the eight wires n the cable split in four pairs. Your Pc talks on two of those wires and it listens on two other wires. The switch (the box that several PCís can plug into, listens to the two wires the PC talks on and talks on the two wires the PC listens to. Since they have agreed which to listen on and which to talk on and both are not doing same on the same pair communications occurs. The Wire we plug between the two just matches both ends of the cable the same and so it is straight-thru.
However, if we want to connect two PCs together to talk to each other, for instance for gaming or to transfer files from one machine to another, we have a problem. Both machines use the same wires to talk on and to listen on. Communications canít occur. The cross-over cable switches the two wire pairs and then each machine talks on different but listens on the correct pair. Now communication occurs.
Very seldom will the average computer using need a cross-over cable, almost always a straight thru works. But occasionally as I mentioned in specialty games or transfer information a cross over cable may be needed.