Timeline shows each item of your website in the order it is requested, along with the status, size, and time it takes to load each request. If you see a specific resource taking longer than expected, you may want to investigate what is slowing down the loading of that item.
Action recommendations can help you improve Page Speed for your website. Look for High Priority recommendations first with a poor Score. Click on "Learn More" for details and links to resources for implementing the recommendation.
Completed recommendations have already been implemented for your website. Click on "Learn More" for details and links to resources for implementing the recommendation.