The MAC address or physical address for a computer is like the social security number for a person. It is a unique ID for the computer's network card or cards. Normally there are MAC addresses for a LAN or wired connection and for any wireless cards your computer may have, for example for a WiFi or Bluetooth connection.
1. To get the MAC address for a Mac OS computer, go to System Preferences and then "Network".
2. On the left hand side, choose the network connection for which you are trying to get the MAC address for, and then click on "Advanced" on the lower right hand corner.
3. Next click on the "Hardware" tab. You will then see the MAC address for the card/connection you chose on Step 2.