Hello mickeymaces and welcome to Apple Support Communities.
It appears you may be having some issues with webmail after a recent Safari update.
Are you able to sign-in to the Yahoo service via their web portal?
If not, you may need to change the password. You'll find instructions for doing that on the Yahoo site itself.
If this is not about webmail, please describe what you are trying to download from Yahoo and what happens when you try. Remember that the more specific info you can provide, the better the chances that someone in the community will be able to help out.
Finally, it appears that you may be running an older version of macOS High Sierra. The most recent version is 10.13.6.
To see if you have updates available, go to System Preferences > Software Update. If your Mac is able to run a more recent version of macOS (Mojave or Catalina), you will see a link for doing that. If the Mac can't go past High Sierra, you'll see an option to update to the most current version of that macOS.
If you have reason to need to use High Sierra such as having older 32-bit apps that you need and you are presented with the option to update to Mojave or Catalina, look just below that and you'll see a link called Other Updates. Clicking on this should allow you to update to 10.13.6.
Cheers.