By connecting your Yahoo account with your Facebook account, you are basically increasing your list of contacts on Yahoo. To get this done, you need to access your Yahoo account settings on a desktop computer. Since October 2016, you can no longer connect Facebook and Yahoo to the Yahoo app.
Step 1. Open Yahoo's website
If you are not logged in yet, please enter your name and password first.
Step #2. Click on Mail
You'll find this option in the top-right corner of your Yahoo page.
Step #3. Click on the gear for settings
You'll find this icon in the top right corner of your Inbox.
Step #4. Click on Settings
Step 5. Click on Accounts
Step 6. Click on 'Connect' next to Facebook
If you're not already signed in to Facebook, you'll be prompted to do so now.
Step 7. Click Continue as [your name]
Step 8. Click OK
Your Yahoo and Facebook accounts are now connected!