Cookie Control is simply a mechanism to enable you to comply with UK and EU law on cookies. You need to determine which elements of your website are using cookies (this can be done via a Cookie Audit ), and ensure they are connected to Cookie Control.
An API Key is required to use this module. This can be obtained for Free by following the download link.
Unfortunately it just doesn't work on my site. When published in the wrong template position a message appears indicating the correct position. When published in that position it simply doesn't appear.
Looking at the help forum there are lots of comments from Joomla users having issues with getting it to work. Many of the posts have gone unanswered.
Verdict: a well meaning attempt to provide a Joomla implementation of the CIVIC cookie control. but one that is neither robust nor supported. I gave it an average rating because it seems it does work for some people and I do like the styling etc.