the main purpose of the turbine in the turbojet engine is to?

The turbine rotates the compressor, compressing the inlet air. Often, electrical generators and hydraulic pumps are attached to the turbine via gears also.

drive the compresser

Correct! The main purpose of the turbine in a turbojet engine is to drive the compressor. The compressor's function is to compress the incoming air, increasing its pressure and density before it enters the combustion chamber.