Add this (immediately after the ServerName directive):
{{Text|
<VirtualHost *:80>
ServerName app
ServerAlias app.YourDomain.lan
ServerAlias username.yourhda.com
</VirtualHost>
}}
You can add more server aliases if you want to access the app under those names (for example: ServerAlias myphotos.DomainName.com). Once you are satisfied with the server aliases, you may save and quit nano by following these steps in Windows: