Net::IRC is a bot framework -- a collection of roles and classes that make it easy to create and extend IRC bots. The core functionality handles the basics of connecting to and communicating with IRC servers, parsing the IRC protocol into a series of events, dispatching these events to the proper modules and methods, and so on.
Most of the "visible" functionality that a given bot provides is captured in a collection of modules, each responding to specific events or commands from other IRC users. For example, there are stock modules that provide a help system, deliver delayed messages, track recent user activity, send random silly messages, and so on. When instantiating a new bot, the user selects and configures the appropriate modules, and Net::IRC::Bot does the rest.
Likewise, to extend a bot's functionality, the user creates new modules that react to new events or commands appropriately. Here again the framework tries to help -- almost all of the IRC-specific boilerplate is abstracted away, leaving just the essentials to be implemented.
The skeleton of the framework is Net::IRC::Bot, which creates and manages the IRC server connection, arranges for incoming IRC messages to be parsed into events, and dispatches these events to modules interested in them.
The initial IRC messaging parsing is done by Net::IRC::Parser::RawEvent; the resulting raw parse is handed to Net::IRC::Bot's !dispatch method, which expands it into a full Net::IRC::Event and passes it to matching low-level IRC event handlers. A fair few of these are provided by Net::IRC::Handlers::Default, which provides the basics to be a good IRC citizen, track joins and parts, and so on.
After the low-level handlers have had their turn, high-level events such as PRIVMSG and NOTICE are dispatched to appropriate methods of all active modules. For example, when a NOTICE message is received, !dispatch attempts to call the .noticed method of every module that has one, handing each the full Net::IRC::Event object. (I say "attempts", because it is idiomatic for action methods to use where clauses limiting the events they will be called for.)
To make it easier to write these modules, Net::IRC::CommandHandler provides a bit of extra scaffolding for writing commands, such as 'help' and 'tell'. Finally, Net::IRC::TextUtil provides a few functions to handle common formatting tasks so that each module doesn't need to write its own.