Lenovo A2107A - Manual (Page 5)

Manual Lock
If you do not need to use your IdeaTab temporarily, you can press the Power
button for about 1 second to deactivate the display. Your IdeaTab will then be
locked, and will enter standby mode.
Screen Unlock
When in standby mode, press the Power button on your IdeaTab to activate
the display. Then, tap and hold the lock icon, and drag the slider over the
unlock icon, as shown in the illustration below.