(...and remember Perl's Motto: "There's more than one way to do it" per Larry) The Running Kernel operates through primordial finite-state machines constructed from another set of abstractions ruled by the POE::Session architecture.
This state machine acts to encapsulate a wide range of generic event driven threads allowing much tighter tracking along the execution path than the relatively informal POE::Session.
Wheels, like Sessions and Loops are built from a uniform set of abstractions - POE::Wheel - that sit on top of the Kernel.
There are seven highly specialized and well-defined Wheels in POE's base distribution: Drivers do the actual work of reading and writing filehandles.
Some of them facilitate higher-level communications between modules, especially stand-alone applications that need to remain independent from the main distribution of Perl.
In general, POE Components are ready-made high level procedures that perform specific large tasks.