DC to DC converters

Whats the purpose of DC to DC converter. its usually used in high frequency circuits. i guese it is used to remove the frequency components add ons to the DC but i am not sure. please if anyone knows tell me.

here's a good start...

https://en.wikipedia.org/wiki/DC_to_DC_converter

i think that DC 2 DC converters usage is maybe to get a greater amount of voltage...

Or a lower voltage and higher current.

It's used to condition the raw power to make it cleaner, with a tighter voltage when efficiency or increasing the voltage is needed (a linear regulator is less efficient and can only step down voltage). That said, a linear regulator is better at making a cleaner output because a DC-DC converter adds it's own switching noise to the output.

And it can't make power from nothing. Increasing the voltage means lowering the output current (or increasing the input current) and decreasing the voltage means increasing the output current (or lowering the input current).