Address

The MAC Address is the PHYSICAL address of the NIC, and so is used by the physical layer in the OSI model. Ethernet uses these addresses to uniquely address machines on your network.

NETWORK layer addresses are used to allow networks to be split into segments and allow packets to be routed between these segements.

If you use TCP/IP as an example the IP address is only really used to work out whether the desination address is local or remote to the sending station. From that point on ARP (Address Resolution Protocol) is responsible for finding the MAC address associated with every IP Address on the ROUTE that the ethernet packet must travel.