There are probably more topical resources for POE help, like POE's mailing list or irc.perl.org channel #poe, depending whether you prefer long-form answers or quicker, specific assistance. There's also POE's wiki, which includes this introductory article and a Cookbook with several examples.

POE is a callback-based event reactor. When something happens, such as when data appears on a socket, POE's Kernel notifies your code that it can safely read from the socket. POE::Kernel's API hides the details of several event loops, including low-level loops like Ev, and high-level graphical toolkits like Prima.

POE's callback model may be confusing because it's name-based rather than code-reference based. Named events make certain things easier, like mapping events to any kind of callback, and dynamically loading or reloading callbacks as needed. Some people store their objects in a database and load them (or reload them) as needed. Most people don't use the feature, though.

POE::Session objects do a few different things, but they mainly act as namespaces for events. Multiple parts of a program can use the same event names, as long as each has a separate session. For example, multiple classes might use the same event name. It would be bad if they got each others' callbacks.

That's a very basic, very high level synopsis of the two main POE classes. If you have more specific questions, I'll be happy to try answering them.