Hey Digamber!!! DFU stands for Device Firmware Upgrade and this Mode is a state that allows you to put your iPhone to interface with iTunes, but does not load iOS operating system or boot loader.
That’s the main difference between DFU mode and recovery mode.
This Mode can be used for multiple things including
-upgrading firmware,
-downgrading firmware,
- and even rebooting your tethered jailbroken device

Process for putting an Iphone to DFU mode:
-Firstly Plug your iPhone into your computer and open iTunes. It doesn’t matter if your iPhone is on or off.
-Press and hold the Sleep / Wake Button and Home Button together for 8 seconds.
-After 8 seconds, release the Sleep / Wake Button but continue to hold the Home Button until iTunes says “iTunes has detected an iPhone in recovery mode.
”iTunes has detected an iPhone in recovery mode
-After this Let go of the Home Button. Your iPhone’s display will be completely black if you’ve successfully entered DFU mode.
If it’s not, try again from the beginning.
-Restore your iPhone using iTunes.

When you DFU restore your iPhone, your computer erases and reloads every bit of code that controls the software and hardware on your iPhone.
There’s the potential for something to go wrong.