EV3 Brick. Turning Brick Off

EV3 brick has 6 buttons (see diagram 1 below)

To turn on EV3 brick, press (2) middle button

The buttons
(1) Back button
(2) Enter button (also to turn brick on)
(3) Up, Down, Left, Right buttons

Diagram 1

The EV3 automatically turn itself off when left alone for some time.
To turn it off yourself, press the buttons labelled (1) (2) (3) in seqence as labelled in diagram 2 below:

Diagram 2

(1) Press corner button till shutdown screen appears
(2) Press right button one time to select check mark
(3) Press center button to turn off

If after pressing corner button (1), shut down screen not visible, keep pressing till shut down screen eventually appears, then follow the above sequence.

Source: Education Robots for Absolute Beginners - EV3 by Prof. Jennifer Kay.

Watch Prof. Jennifer Kay's video below for greater details