Its important that before you start writing your own Plugins for Syn Virtual Assistant you get some knowledge as to how Syn Engine works.
To do this we recommend you to ( atleast ) create a simple Natural Language Application using Syn Engine by following tutorials for Syn Engine. Once you have successfully created an application you will have enough knowledge to create your own custom Plugins.
You shouldn't assume that Plugins and Applications are 2 different things. They maybe physically but they follow the exact architecture and conventions used for interacting with Syn Engine. Syn Engine was designed with Virtual Assistants in mind and so most of the tutorials should fall in favor of Plugin development.
To create your first Natural Language Application. Start Here