So ...

Upon activation, simply go to your media library and upload your image and the audio file you want to add to the image:

After uploading both files, you'll notice a new "Audio Story" column on your Media => Library page (if needed, click on the list view icon to display your media files in a list). You'll have to click the "Attach" link next to your image file ...

... to access the popup window where you can select the audio file you want to attach to the image:

Simply click the "Select" button and the plugin will link your image and audio file to each other:

And that's it ... Now that your image is linked to the audio file, you can add it to any post or page ...

So let's see the magic ...