If you are just wanting to hook them up together you can simply use a crossover cable to connect them up directly to the Ethernet ports. But if you want to allow them both to access the internet you need to get a router. There are plenty of articles in TechSpot describing them thoroughly. Have a look around.
ROM
Yes it is possible to connect two computers together
The Internet is a network of web pages on servers that computers can connect to if they have the address of the web page. Computers CAN connect to each other using an internet connection, but that is NOT the main use of the internet.
It is when 2 computers connect directly with each other. No wireless router between them. When you set up you NIC it will have an option for ad hock mode.
If you want computers just to communicate with each other. The answer for question would be yes.: Via Cat Cables :D
Everything relates to science. the way computers can connect each other, that's science. all the weirdo jumbo gear inside your computer, thats science.
By using a router with DHCP turned on in the router
Networks are most often used to connect one or more computer systems to each other, whether to fulfill tasks that require more computers or to share data between the computers. A wide area network can connect more computers than normal networks.
They (the computers in the network) connect to each other through a computer protocol (a fancy name of say rules that a computer follow to talk to each other) called bittorrent.
Depends on how many switches each router takes. You need a router to connect all the other routers, and then enough switches to make 81. For example, you can use 6 16 port routers to connect the computers and 1 8 port router to connect those routers together
You can use wireless network cards to connect two computers to the same network so you can play computer games. Another way to connect two computers is to use a crossover cable between them using the Ethernet ports so they see each other and assign an IP address.
Buy a lan router, they can be used with lan cable or wireless to connect all your computers through a network. If there are only two computers that you wish to connect then you only need on lan cable which you connect in the back of each of those two computers to create a network.