Most of the Microcontroller,s Require 5V DC as in input to work properly to get this constant 5v Dc simply we can use LM7805 ic it will give us a 5v DC but it,s not an efficient way because this ic Can produce too Much heat it would required a Bulky heat sink other wise it will burn out.
Boost Mean to Step up the Dc voltage to some Usable level.
Always use LM2596 Buck converter it is more efficient as compare to LM78XX series the good quality of LM2596 is you can set your desired Output voltage with the help of potentio meter by using this you can make a charger for your Mobile phone in 5 minutes
IN + = 12V
OUT + = 5V