Ethernet is the most popular and considered the networking topology standard for most computer connections. There have been many kinds of Ethernet, but the most popular is 10/100Mbps running over copper twisted pair wires. 100Mbps Ethernet is also called 100baseT and Fast Ethernet.

Connections between 10/100 Ethernet adapters are made using cables that run to an Ethernet HUB or Switch. Hubs electrically connect your computers together and switches act like traffic cops making your network more efficient.

When only two computers are present, a special kind of Ethernet cable can be used called a CROSSOVER cable.

More about hubs and switches

10/100 Ethernet cables have 8 wires, of witch 4 are used for data. The other wires are twisted around the data lines for electrical stability and resistance to electrical interference. The cables end in RJ-45 connectors that resemble large telephone line connectors.

Two kinds of wiring schemes are available for Ethernet cables. Patch cables and Crossover cables. Crossover cables are special because with a single cable, two computers can be directly connected together without a hub or switch. If a cable does not say crossover, it is a standard patch cable. If you are connecting computers to a hub or switch, you need patch cables

There are also different grades of cable quality. The most common are CAT5, CAT5e and CAT6. CAT5 is good for most purposes and can transfer data at 100Mbps. CAT5e is rated for 200Mbps and CAT6 is rated for gigabit Ethernet. I like to run CAT5e whenever possible because there is usually not a cost difference from CAT5 if you look hard enough.

For all twisted pair Ethernet, 100Meters is your maximum distance.More about maximum distances   

When 100Meters is not enough distance, an Ethernet to fiber media converter can be placed on each end making the maximum distance something like 40Km (See the Example here).  Another use for fiber is electrical insulation.  Some people like to run cables underground between s.  If you run CAT5 cable, the s have different 'ground potentials' and you will burn out network card during any electrical storm.  The solution is fiber!  Run fiber between the s or run a pair of fiber converters on one end of the cable with a short fiber run.  This will electrically separate the two s. 

PCI and ISA Ethernet cards are highly sensitive to IRQ conflicts.  If your card is not operating correctly, check for an IRQ conflict