FastBoot is a way to quickly upgrade each partition package of Android.It is a brush mode of connecting devices with USB cable.
Input the following ADB command:
adb reboot fastboot
To use FastBoot to brush the machine, you must first unlock the bootloader, otherwise the machine cannot be flashed.
After entering the FastBoot mode, input the following command to unlock:
fastboot flashing unlock
fastboot flash boot /path/to/boot.img
give an example：
After upgrading the firmware, you can choose to lock the device （Not required during debug）:
fastboot flashing lock