This article from the PHPseagull documentation will get you started with the main concepts of the framework. Later in the series will be a practical, step-by-step guide to building your own modules.
Basic workflow in PHPseagull is simple: you create entities and you manage them.
For a discussion on working with entities please see here. Once you have all your entities created you manage them with manager classes. Each module in PHPseagull has at least one manager class, in some cases more complex modules, like Publisher, have more than one manager class because they have to manage a number of entities.
Each manager class must inherit from the Page class which has the following abstract methods defined:
The manager classes override the workflow methods according to the particular requirements of the module.