Claes Gustavsson commented on Need some start help creating an app

Hi Chris
I guess I´m missing something big here, but I don´t understand what an app is, is it just a .liquid page or set off .liquid pages?
Am I suppose to rebuild the shop I created, to an app?
And where do I create them, in the template editor or on my computer and then upload them to shopify?
Is there a very basic sample somewhere, a "Hello World"?
In the app settings what is Application Callback URL (required), Preferences URL, Support URL - are they links to shopify or at my own server?

As you can see, I really don´t get it :-)

The app I´m planning to build is very simple, it needs to add some script tags in the theme.liquid file, add a javascript file to the assets, then the shop owner needs to be able to upload 5 images to the assets, thats it. How and where do I start?

Thanks.