Restore in DFU mode

[JHT]

Could someone please explain in simple terms how you do this please?
Whenever I have restored my phone previously, I have simply plugged it into my PC via iTunes and clicked restore.

 

[Thomasjtsi]

Restoring from DFU mode is usually only necessary when restoring a Jailbroken iDevice. There are some who will say it's not necessary... however, DFU mode allows a cleaner install of the IPSW from a Jailbroken state.

 

[JHT]

My iPhone 5 is currently jail broken on 6.1.2, so if I decided to unjailbreak and upgrade, I would put in dfu mode, connect to iTunes and upgrade?

 

[InkedAdrenaline]

My iPhone 5 is currently jail broken on 6.1.2, so if I decided to unjailbreak and upgrade, I would put in dfu mode, connect to iTunes and upgrade?

Correct, but you can't go back if you do. 6.1.3 is not Jailbroken.