If I understand right, "total clicks" means how many clicks I've got from google's search result. And the table beneath shows a breakdown of how many clicks I've got from each key words. Intuitively I'd think the "Total Clicks" number is a sum of all the clicks in the table below, but it is much bigger, why is this?
It's simple way for GWT - if you add up the clicks of the individual keywords about 50% of the clicks are missing. Because, Google gives some reasons here (some of privacy reasons) but they can hardly explain the (huge) differences. And some of the keywords search volume is very low can be a reason also.
You have to connect with Google Analitys for clicks & visitors details.
For details please visit: https://support.google.com/webmasters/answer/6155685?hl=en