Need to know about permanlink

hello guys
I am really curious to know about permalinks. made website 3 months ago and that time i dont know much about blogging. But now after few research i come to know about permalinks. my permalink is set to default. But my friend suggest me to change my permalink to .html. he said google give more preference to .html. Now after i change my permalink to html All my before sharing link showing 404 error and also when i search on google my keywords and my go to my website its showing 404 Error.
Now i need to ask you will google soon update my website and my website reputation will be down by google as many share links will show 404 Error.

PLz suggest me

Change your permalinks to post name in your WordPress settings and remove the .html to resolve the 404 issues. If you don't resolve it quickly enough, and Google spiders your website only to discover that all your pages are 404 pages, you could lose your rankings.

Lastly, Google doesn't give any preference to .html pages. It's just a fallacy.

Change your permalinks as soon as before google crawl your site. If you want .html only you can redirect your old address(without .html).

Change your permalink to post name in your Wordpress settings and remove the .html resolve the 404 issues.