How to add javascript to customise a form with a slider


#1

How to add javascript to customise a form with a slider?
For example:
http://immobilienanlage.hfh.de/test-2/ 

this article shows the code but, how do I add it?
https://community.unbounce.com/unbounce/topics/forwarding_a_slider_amount_to_a_hidden_field?topic-re…

I have added it to the javascripts, before body end tag, but then what?

much appreciated!