The documentation here covers the latest version of core Speck content management system at the moment. Sorry, but we haven't managed to find the time to fully document the portal framework as yet (though we are working on it).
If you are new to Speck, going through the process of creating a simple Hello World app won't take long and will give you a good idea of how the core system works, where files are stored etc., without trying to learn anything fancy like how to create content and property types. The Sydney Jabiru sample app builds on the hello world app and provides a demonstration of some other features of the core content management system (revisioning and promotion in particular). Once you've gotten your head around all that, check out the features added by the portal framework by giving the demo app a whirl (the demo makes a good starting point for new applications btw).
If you are already using Speck and are trying to find out how to customise and extend it, all of the sections within Building Applications should be useful, especially the Creating Content Types and the Built-in Property Types pages (properties are used when creating content types).
If anyone has anything to add, or has noticed any mistakes or typos, please get in touch with us and we'll add/fix it.
Note: some screenshots in here are very old, but the documentation is otherwise up to date.