You must know that no one here has time to explain step by step to you because the matter is complex and depends from web page to page as well as the platform it is on.
I can only give you a few links and on some of those pages you can click for additional info
- Hardenize: Comprehensive web site configuration test
- https://pagespeed.web.dev/analysis/https-www-logseo-net/k975zc4di7?form_factor=desktop
- Yellow Lab Tools - Page Speed audit
- https://validator.w3.org/