Gandora on "Make plugin out of javascript slider"

Hello everyone,
I need help with making a plugin that applies a javascript to images/divs.

The script is some kind of slider. Here's an image of a big picture of which only a part is shown and it's thumbnail.
Sample Picture

So, apart from not having been able to figure out how to add a js-script (and where to place it) I would like to be able to choose the big picture on the wordpress dashboard/admin page, in the plugin menu from the media library (and maybe have some automatic resizing for the thumbnail? Or should the library just contain a thumbnail picture which has to be chosen as well?).

Here are my php-file in the plugins folder, and the script I want to apply:

Php-File
JS-Script

I copy pasted amost of the PHP code and adapted it a little, so I know that the 'add_action' call should not be done for the 'admin_menu'. But I also don't know what I should replace it with.

Any help is highly appreciated, since I'm struggling with wordpress for two weeks now.