Enable USB Debugging and OEM Unlock

To enable USB Debugging

You will need to become a Developer first on your device !!

To become a developer

Unlock your device and go to

Settings » About Phone » Build Number or Version » Tap seven times

You will get a message that you are a Developer.

To Allow USB Debugging

After completing the above steps and becoming a developer on your device go to

Settings » Additional Settings » Developer Options » Toggle Developer Options to enable » Toggle USB Debugging to enable

On some devices the path may be as under

Settings » System » Advanced » Developer options » USB Debugging ( enable it here)

Return to main screen

To unlock OEM

Why do you need to enable `Unlock OEM`

To flash a custom ROM like LineageOS or /e/OS you need to unlock the bootloader of your device. This requires that you as the owner of the device should

Grant permission to unlock the bootloader
Unlock the bootloader

To know what unlocking changes on your device, and whether you can lock it back afterwards, read Bootloader relocking.

Steps to enable `OEM Unlock` through the `Developer Options`

Settings > Additional Settings > Developer Options > Search for OEM Unlock and enable

On some devices the path may be as under

Settings » System » Developer options » Search for OEM Unlock and enable

Steps to enable `OEM Unlock` through the command line

Enable USB debugging on your phone and connect it to the pc by a USB cord. The instructions for this are given above
Open a console window
Enter adb devices
Proceed only if your device is detected.
Enter adb reboot bootloader
Enter fastboot devices, proceed only if the device is detected
Enter fastboot oem unlock
You will be asked to confirm the request on the phone screen, select yes
When the process completes, type fastboot reboot and the phone will reboot normally.