So to test the performance of a web page, you have to do the following steps:

• First open the webpage on your browser.
• Then right click anywhere on the page.
• Select Inspect.
• A small window opens up on either the right side or bottom of the screen.
• On this window, choose the tab called Lighthouse.
• Then select either mobile or desktop.
• Then select Analyze page load.
• The performance of the page will be displayed in few seconds.
• Other values like SEO, accessibility, etc will also be shown.
• Make sure that you stay on the webpage when the page is being analyzed by Lighthouse and don't navigate away until you get the results.
• Sometimes the performance percentage might be affected by certain issues and so you have to test the page in an incognito window.