The complete and up-to-date user manual of Synfire Sparks, Express and Pro can be found on the Help menu of the application or online here.
You should definitely use the search function of the online version, if you are looking for something specific. While in the running application, you can open an interactive browser with Help >> Embedded Help and simply point your mouse to the objects you want to learn about.
There is currently no PDF version of this due to technical issues. We are trying to fix it.