My Yahoo and other sites do not load. I have a MacBook Air. How can I

Try suggestions given in this article.

https://support.apple.com/guide/safari/if-you-cant-open-a-website-ibrw1071/mac

If this doesn't help:

 Download EtreCheck: https://etrecheck.com/  and post the report here.

 Click, “Free Download” button and then  “Click to download” button,

 open Downloads folder, click on it to open, and then select ”Open”.

 Choose a problem” from the popup menu box, and then “Start EtreCheck” in the dialog.

 Click “Share Report” button in the toolbar and select “Copy report”.

 Click the “Page” button in the toolbar at the bottom of this page and paste it when you reply.

 Note: This is a diagnostic test.