What program to use to add drag and drop functionality within a webpage

I'm looking for guidance on where to begin looking for a way to add drag-and-drop functionality within a web page. I know very little about web page development, so any insight is appreciated. What I am wanting to build is a web page that will have objects (e.g. image thumbnails) in a side pane that you can drag and drop into the main window to lay out how you want. In my case it will be in a structure like a binary tree where each image can be dropped in as a parent or child of the existing nodes. Where should I begin looking for a program that will allow this type of functionality? I have experience with Python, so I was hoping something like Django might do the trick, but since I know so little about web design, I really don't know if that is the right place to begin.