This is a protocol/tool that is used for writing data directly to the device’s flash memory. In practice, Fastboot is used to flash recoveries, bootloaders, and kernel to Android device. In Fastboot Mode, you will be able to restore backups, change the splash screen, and also flash system updates.
How to open Fastboot on Android? How to use Fastboot with PC?
Most of the Android devices will get into Fastboot Mode by using the following instruction:
Press and hold your Power button.
On your screen, touch and hold Power off. Confirm by OK, if needed.
Turn on by holding the Power key and Volume Down buttons.
At this moment, when Fastboot Mode is on, connect Android device to PC by using the USB cable.
After that open up the terminal prompt on the computer.
Now, you will be able to find the device's Serial Number on the PC list.
If you are getting problem in order to open Fastboot Mode on your smartphone then the best solution is to go to the HardReset.info YouTube Channel Fastboot Mode Playlist to find a tutorial on your own phone model.
What do you need to use fastboot for?
Fastboot Mode is an amazingly helpful tool, where you can accomplish many useful operations such as:
unlock/relock bootloader,
flash a custom recovery,
flash a custom ROM,
flash radio,
flash kernel,
change the splash screen,
restore Android backup.
In the tutorials below, you can check how to open Fastboot Mode:
This is a protocol/tool that is used for writing data directly to the device’s flash memory. In practice, Fastboot is used to flash recoveries, bootloaders, and kernel to Android device. In Fastboot Mode, you will be able to restore backups, change the splash screen, and also flash system updates. 
