The HowStuffWorks web site has an excellent article describing Ethernet basics. The Lantronix and CISCO DocWiki websites also offer free tutorials about Ethernet technologies. If you prefer video training, YouTube and the Comnet product training video websites both offer good training videos about Ethernet.
Ethernet is a popular local-area network technology used to connect a number of devices such as computer and printers within a relatively close physical area. These devices are called nodes. While early Ethernet networks used coaxial cable as a shared medium to connect nodes on the network, more recent implementations use twisted pair or fiber optic cable and hubs or switches to connect Ethernet segments in more complex configurations.
Ethernet is the data link layer protocol in the TCP/IP stack that details how data is transmitted from one networked between nodes. Each node on an Ethernet is assigned a Media Access Control address. No two nodes on an Ethernet can have the same MAC address. Information is sent through the network in small packets of data called frames. These frames include both the source and destination MAC addresses.
The Ethernet protocol uses carrier-sense multiple access with collision detection, often known as CSMA, to control communication between nodes. CSMA "listens" to the medium to determine if a frame is currently being transmitted across the network. If the medium is quiet the node sends its frame across the network. Occasionally, two nodes send a frame at the same time and a collision occurs. Using collision detection the nodes recognize a collision and then pause for a random amount of time before using CSMA to resend the disrupted frame to the destination node.