Step 1: exhaust energy drives the turbine
As cylinders fire, hot exhaust pulses travel through the manifold into the turbine housing. The turbine housing directs this flow onto the turbine wheel. The shape and size of the turbine housing affects response, backpressure and high-rpm flow.
Step 2: the shaft spins the compressor
The turbine wheel and compressor wheel share a shaft. When the turbine accelerates, the compressor wheel accelerates too. The compressor draws air through the intake, compresses it and sends it through charge piping to the intercooler and throttle body.
Step 3: the wastegate limits boost
Without boost control, the turbo may keep accelerating until pressure becomes unsafe. A wastegate bypasses exhaust around the turbine once the target boost level is reached. That can be an internal wastegate built into the turbine housing or an external wastegate mounted on the manifold or turbine inlet path.
Step 4: the tune makes it safe
The ECU or standalone engine management system must add fuel, control ignition timing and manage boost targets. A turbo setup is only as safe as its calibration, sensors and mechanical condition.