Try this:

- Open settings
- Click on Accessibility
- Click on Advanced settings
- Check that "Speak keyboard input aloud" is turned OFF. 

settings wont open

If you enable the TalkBack shortcut, you can turn the feature on and off by pressing the volume up/down keys at the same time.

If you have Google assistant turn on, you can tell google assistant to turn off Talkback.

You can also swipe down the notification bar from up top to get to settings.

Note you will need 2 fingers in order to swipe