The Sprint Retrospective is an opportunity for the Scrum Team to inspect itself and create a plan for improvements to be enacted during the next Sprint. They can help team reflect on their behavior and also provide information to improve.
Recently I wrote and article about this and I was fortunate to get it posted on Scrum Alliance website.
Below is the link to the post.
https://www.scrumalliance.org/community/articles/2017/may/retrospectives-and-what-they-can-tell-us