Has swipe to unlock on your tablet or phone stopped working? Do you have green squares appearing and a voice? Maybe you pressed and held down the volume button by mistake instead of switching on. This has activated TalkBack mode. In theory pressing down the volume up/down buttons together for 3 seconds should turn it off again but if this does work then it becomes more difficult. Another way is to say “Hey Google”, then say “Turn off TalkBack”.
If this does not work then you will need to navigate to the TalkBack option in settings, accessibility but to navigate there with TalkBack switched on can be tricky. You will need to double tap within the green box to unlock the screen and navigate to settings. Use two fingers to drag the green box to accessibility, double tap it then navigate using 2 finger drag to talkback. In talkback you can double tap on the “on” button to switch it off.