Select the project, and choose Add -> New Item from its context menu or the Add New Item from the Project menu, then the following dialog will appear:
Choose the Revit Addin from the Categories pane and click on the Application Event Handlers on the right Templates pane, and give a new name for the item source file or accept the default one.
The welcome page will show up:
Click the Next button to continue and the Application Events page will come out:
Please check some events of interest and click the Next button again to continue. The following Event Handlers page will show up:
In this page, the event handler class name defaulted the same as the source file holding it can be changed, handler naming convention can be specified, the External Application to register (and unregister) the event handlers can be chosen, and whether some default responses will be added to the handlers can be opted.
After the Next button is clicked one more time, the summary final page will give you a chance to review all options that have been set for the Revit Application Event Handlers, and if necessary you can go back to previous pages to make changes or even cancel the whole process.
When the Finish button is pressed, the Revit Application Event Handlers will be created, registered (and unregistered) in the right places, and have some default message responses if applicable.
The new project item wizard is packaged into the same installation of the RevitAddinWizard.
Links to some related articles: