Spark is a plug-in based application. Each type of Action is defined in a plug-in. Spark Action plug-ins have a ".spact" extension.
Spark has some built-in plug-ins but it is also possible to add other plug-ins by copying them in your Library folder.
If you try to open a plugin with Spark (by double clicking on it for example), Spark will propose you to install it.
You can also add a Spark plug-in by copying it in "Application Support : Spark : PlugIns" folder of your Library folder or in the Computer Library folder.
Spark contains 5 built-ins Actions plug-ins:
Help for each plug-in can be obtained in the Help Menu in Spark.