Air Drop is a great feature that allows you to easily transfer file between computers without having to know that name of the computer or the IP address. Air drop will automatically detect all other Macs on the same LAN running air drop.

Air Drop is not supported on older MACS even if you have OSX Lion or newer.

Figuring out if your MAC supports Air Drop:

If you Mac is the same or newer than the list below then your MAC supports Air drop. Running OSX Lion or newer.

MacBook Pro (Late 2008 or newer)*
MacBook Air (Late 2010 or newer)
MacBook (Late 2008 or newer)*
iMac (Early 2009 or newer)
Mac Mini (Mid 2010 or newer)
Mac Pro (Early 2009 with AirPort Extreme card, or Mid 2010)
* The MacBook Pro (17-Inch Late 2008) and the white MacBook (Late 2008) do not support AirDrop.

Good news is that you can enable Air Drop on an older MAC that is running OSX Lion or newer running the following command inTerminal.

Accessing Terminal:
In the Finder Applications>Utilities>Terminal

In the command line in terminal type the following command:
# defaults write BrowseAllInterfaces 1