optimization - configuring e-tags -

I am using Yslow as a simple speed benchmarking tool and I actually came across a misleading concept of e-tag

The main problem is that: How do I configure e-tags? My grade in YESLO says:

There are 19 components with incorrect configured entities

  * http://thehotelinventory.com/media/js/jquery.min.js * Http: //thehotelinventory.com/media/js/jquery.colorbox.min.js * http://thehotelinventory.com/media/js/easyslider.min.js * http://thehotelinventory.com/media/js / Jquery .tools.min.js * http://thehotelinventory.com/media/js/custom.min.js * http://thehotelinventory.com/media/js/jquery.validate.min.js * http: / / Thehotelinventory .com / media / images / colorbox / loading_background.png * http://thehotelinventory.com/media/images/productheaderbg.jpg * http://thehotelinventory.com/media/images/buttons/field-bg // Etc  

Developer on Website Optimization Browsing through the Yahoo.com guidelines, I can not really understand the thing with e-tags

Shows how to disable ETags for IIS and shows how to do it for Apache.