the wastegate is just a disc on that pivot that covers a hole that allows exhaust gas to go straight from the manifold to the downpipe bypassing the turbine. the spring and preload in the wastegate holds it closed to build up boost, but the boost pressure then pushes against a diaphragm in the actuator to overcome the preload and spring force and push the wastegate open. this allows exhaust gas to bypass the turbine and not spin it any faster to not make more boost.

hth.