The compressor wheel spins and creates boost. Most modern turbochargers use billet aluminum compressor wheels, CNC machined from forged aluminum. The larger the compressor, the more airflow and HP will be attainable.
The turbine powers the compressor. Turbines consist of a wheel and a housing. They can be undivided (single scroll) or divided (twin scroll). The material used for the turbine wheel and housings depend on the application; Drag racers tend to prefer inconel. Road race and Drift applications prefer gamma-ti and Mar-M.
The wastegate controls how fast the turbocharger spins. Wastegates can be internal or external. Pneumatic or Electronic.
The bearing fills with oil and allows the turbocharger to spin at extremely high speeds. 100krpm is typical for a high boost racing turbo and 200krpm+ speeds can be reached by smaller turbos.