You need to understand that a turbocharger's wastegate actuator opens when boost pressure is applied. An open wastegate holds your boost level at that point. A closed wastegate does nothing to regulate pressure. An engine at idle doe not produce boost. When you accelerate or induce a load on the engine, exhaust flow spins the turbine which compresses air to produce boost. By diverting exhaust flow away from the turbine and out the exhaust you regulate the boost pressure. This is the function of the wastegate and its actuator. The wastegate actuator controls the position of the wastegate and how much of the exhaust flow is used to produce boost.
The wastegate actuator is a simple mechanical device. Pressurize the hose leading to it and it begins to push open the wastegate. In the examples below we'll assume the wastegate is fully open at 10psi. As boost reaches 10 psi the waste-gate is open and you're not going to get any more boost. Looking at the first diagram, the path of airflow is show by the red line. (The BoostValve is set to an opening higher than 10 psi so its still closed and not passing boost pressure or bleeding out any air to atmosphere). The VW's N75 boost solenoid is passing all air through it and directly to the wastegate.