Synchronous Buck Converter Mathematics
This is the simplest and easiest switching converter to understand: -

The input voltage is modulated by the switch's duty cycle to produce an average value that corresponds with the required output voltage.

The LC acts as a low pass filter and converts the modulated duty cycle from above into a steady DC value.


There are mathematics involved if you want them to be but the words are simple enough and 100% accurate in defining the operation of two switches selecting either Vin or 0 volts.
If you want the maths of the LC filter then there are plenty of resources for this and a calculator to help you visualize things. The theory is not that involved so I've not bothered to repeat it here but, if you need it or help with it please ask.