Follow these instructions to enable developer options and USB debugging mode.

If you're using a Windows operating system, download the Google USB driver and follow these instructions to install it.

Navigate to this page to prepare the calibration software.

If your phone isn't turned off, do so now.

Hold down the power and volume down buttons on your phone for three seconds to enter Fastboot mode.

Your phone will show a red warning triangle with the caption "Fastboot mode."

Plug your phone into your computer.