What is the function of turbo?

Turbo function is to increase the engine power by adding a certain mixture of air to fuel.

Turbo hlpes to improve engine preformats.

turbo is function to compress the air mixture and give more power to the combustion 

Enhance the engine efficiency by increasing the intake air volume.   

turbo used to unburned air into go through the engine. unburned air is a before compressd air. so no need of extra compression. turbo have two types of valves vgt and wgt

" Of course Turbo increases efficiency of an engine by inducting fresh charge of air  to achieve Maximum fuel energy,  turbo is driven by exhaust gases of the operating engine. In this way we use wasted energy in useful work."

Turbo increase the mass of air which charged to cylinders ,at the same time fuel also can increased to the engine ,so the total power of engine is increased at the same engine size.

Turbo is simply a air compressor it will take much more amount of air(O2) to fully burn the fuel in combustion chamber(Basic principle of with high amount of air(O2) fire capture suddenly).

in a very simple way the turbo charger increase the pressure and the mass of air charge going to the engine so we can get more output power with same cc and it has various types and concepts although it got some weakness points but till now it's most effected super charging methods .

I will add, that turbo ease the function of piston suck in air

The objective of a turbocharger is to improve an engine's volumetric efficiency by increasing density of the intake gas (usually air) allowing more power per engine cycle. Theturbocharger's compressor draws in ambient air and compresses it before it enters into the intake manifold at increased pressure.