When you deploy that Hook (war file) into your server and restart it, in the (bin) logs, you could see one log statement which says that your particular Hook is available for use. This means your Hook has been successfully deployed into your Liferay portal.
To run the Hook or invoke a particular method inside your Hook, you need to invoke the flow for which your Hook was written.
For eg., if you have written a hook for logout.events.post=
and if you want to invoke this, then you need to logout from your portal.
In your case you have written a Hook for registration. So, you need to do registration. Remember your Hook method should have extended Action
class.