In this tutorial, you will learn how to:
• Turn on device
• Turn off device
• Lock and unlock device
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Press and hold the Side button until the Apple logo displays.
Press and hold the Side button until the slider appears. Drag the slider to turn your iPhone completely off.
Press the Side button then press the Home button. To lock iPhone, press the Side button.
Note: iPhone locks automatically if your device is idle for 30 seconds. To adjust the screen lock time, select the  Settings app > Display & Brightness > Auto-Lock > desired lock time.