How do I completely start my iPhone?

To completely restart (power off and then turn back on) your iPhone, follow these steps based on the model you have:

For iPhones with Face ID (iPhone X and later):

1. Press and hold the Side button and either Volume button until the power off slider appears.
2. Drag the slider to turn off your iPhone.
3. Once the iPhone is off, press and hold the Side button again until you see the Apple logo to turn it back on.

For iPhone 8 and iPhone SE (2nd generation):

1. Press and hold the Side button and the Volume Up or Down button until the power off slider appears.
2. Drag the slider to turn off your iPhone.
3. To turn it back on, press and hold the Side button until you see the Apple logo.

For iPhone 7 and 7 Plus:

1. Press and hold the Side button and the Volume Down button until the power off slider appears.
2. Drag the slider to turn off your iPhone.
3. To turn it back on, press and hold the Side button until you see the Apple logo.

For iPhone 6s and earlier:

1. Press and hold the Home button and the Top (or Side) button until the power off slider appears.
2. Drag the slider to turn off your iPhone.
3. To turn it back on, press and hold the Top (or Side) button until you see the Apple logo.

These steps will ensure that your iPhone is completely powered off and restarted. If you’re looking to perform a force restart (which can be useful if the device is unresponsive), the method varies by model as well. Let me know if you need instructions for that!