As you may already know, one of the new thing with the Wave 15 of Microsoft products (Office 2013, Exchange 2013 or SharePoint 2013) is the new way to provide add-in which is now called Apps.
With SharePoint 2013, the documentation is not complete…
If you follow step by step the official Microsoft documentation (http://technet.microsoft.com/en-us/library/fp161236.aspx), you will be able to install SharePoint Apps from the AppStore BUT you will get HTTP 404 error message when you will try to use it.
Also, don’t forget to define a public domain if you plan to use SharePoint App from a public website.
The solution, which is not so difficult but tricky, is:
- Create a new web application running on port 80 with NO HOST HEADER; you can define other settings as you want or keep the default value
- Create a new root site collection for this new web application
Et voila, your SharePoint App is now useable.