The Performance section provides you with a more comprehensive explanation of each metric and recommended values. If you want to see more information, just enable Metric details:
This page helps you indicate key metrics of how your website is performing - so you can have a clear goal on what to work on. For improvement - follow recommendations in the Structure tab.
You already saw the Top Issues of your website - the Structure section will show you the full list of them and the potential improvement if you eliminate them. We recommend addressing High and Medium issues first while leaving Low ones for the end.
Clicking an arrow near a listed issue will provide you with all the needed information about the problem. From there you can click on Learn how to improve this and check what GTmetrix suggests for fixing it:
In case you are using WordPress you can refer to these tutorials for tackling the most common optimization issues:
Here are some tutorials for other Content Management Systems or custom websites:
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