To get started with the osax you installed, the first step is read its documentation. Most of osaxen will include a brief document explaining the usage of its commands, and some test scripts showing the capabilities of the scripting addition.
After installing a scripting addition, you can start using it immediatelly. You can drop the osaxen onto your favorite script editor’s icon and it will show you its dictionary. In OS X all script editors include a menu item which will allow you opening the dictionary of any scripting addition installed in your system, usually located under the “File” menu.