ok shortly turbo charger hv 2 main parts ie impeller and turbine.so exhaust gases instead of geting out goes to rotate the impeller which connect dirrect to tubine by a shaft.then the rotation of impeller cause the tubine also to rotate.The ratation of tubine suck more air from the cleaner and increase the volume of air in the cylinder.as the volume increased the power also increased then engine efficiency increased indeed.NOTE no fuel used to operate the turbo charger.