Fastboot Basic commands for Flashing Custom Roms, is the another thing you need to know before flashing your phone.Basically, Fastboot is a protocol, it can be used to change/re-flash the partitions inside the system/phone.This little tool can be found in the same Android SDK folder, where the adb exist.Fastboot is the alternative tool to do the Recovery, Installations and Updates.
Like adb,You can also find the fastboot tool in your Android SDK folder.(Via Andoird SDK Manager, you have to install Tools, completely).You can find the fastboot tool in /platform-tools/ folder.The fastboot file will be named as fastboot.
(Note: Adb tool also, exist in the same folder, named as adb).
In most of the phones, Vol down + Power Off button will get you into fastboot mode.If you are connected in fastboot mode, you can see a andoird repring image on your phone.
Inside the folder /platform-tools/ , Using Shift+right click to open a command shell (In windows) or use the Terminal (In Linux)
(Note: If you are using arch linux or Redhat based os, put a ./ before all the command to execute.Eg: ./fastboot devices. Also, In linux, use command sudo su to gain all the permissions)
Fastboot Basic commands for Flashing Custom Roms are these:
fastboot devices
List of all the devices connected in fastboot mode, in to your system.
fastboot flash recovery recovery.img
Flash the recovery partition of your phone.(Remeber that, the third parameter decide which partition of your phone has to be flashed). In most of the cases, you will flash the CWM (Clockwork Mod)/ TWRP using this command.
fastboot flash boot boot.img
Flash the boot partition of the system/phone.
fastboot reboot
Reboot the phone.
So, these are the Fastboot Basic commands for Flashing Custom Roms.Also, you can find the Basic ADB commands from my another blog post.I hope this helps.