MAC addresses are address that are burned in all network access devices at time of manufacture. They give every network access a totally unique address.
Your device will have a IP address which you will see sometimes for IPv4 addresses that look like 192.168.1.2 Those address apply on the network you are currently connected to and change as you move form network to network. They are sorta like your mailing address which changes for you whenever you move. MAC addresses are like your name, it basically stays permanently with you (you can change but takes legal action like marriage, divorce, or having court change your name) but it basically stays same no matter where you move to in your life.
MAC addresses are 6 bytes long and are expressed in six pairs of hexadecimal numbers. Hexadecimal numbers are base 16 and include 0 through 9 and the letters A through F. 00-00-0c-12-34-56 would be a MAC address. The first half of the address (first 3 pairs) is a number that has been assigned to the manufacturer. If you know your MAC address you can look it up at the FCC website and find the manufacturer of your network device. The last half of the address is a unique serial number assigned by the manufacturer. Using this system all the addresses are totally unique.
The MAC address cannot be changed except on routers. On routers you canít really change the built-in address but you do have the ability to have it use a different MAC address you assign. In large companies this is used when a router fails and a new one replaces it, the new one can be made to look like it is the same router and lot s less work must be done. On home routers this is sometimes done to make a router look like a PC you had when your ISP registered you, and everything leaving your house appears to come from the original PC.