Hi faraday,
if you're talking about Eagle: It has no dedicated "footprint manager".
Any part's footprint is part of a package. Opening a library you can as well open the library containing a certain component or create a new one.
A device contains two parts: symbol (this is used to create a schematic having pins). It further contains a package (this the part with it's footprint, outline of the package and pads (solder pads)).
symbol and package connected with each other make a device, with pins connected to the pads of a package.
Designing a schematic you'll select a device which has all necessary information of a part for the proper connection and - of course - the part footprint.
Boncuk