To get started please have a look at the 'Namespace' or the 'Classes' sections you can see on the top of the page.
The most central classes will probably be clMain.main(), clWindow.winGTK() and clLayouts.Layouts() since these classes handle most of pyjama's actions.
In order to develop Plugins you probably want to have a look at Pyjama's plugin and event interface.
1.5.8