...if a turbo...

[thermal]

just like the top picture indicates, there are 2 sides of the turbo assembly:
1. the turbine side
2. the compressor side

both rides on the same shaft but each have its own separated casing. as the exhaust gas leaves the exhaust port, the expanding gas will initiate a "wind mill" effect to the turbine side. since the turbine is directly shafted with the compressor, the compressor will also spin therefore compressing air. this compressed air is directed to the intake manifold for combustion purposes.

on the other side of the assembly-the turbine side, after the "wind mill" effect occurs, the expanding gases will be directed to the downpipe.

internal wastegate and external wastegate operate on the same function but not necessarily located on the same section of the assembly. for the most part, external wastegates are mounted on the exhaust manifold. internal wastegates are incorporated within the outlet port of the turbine section.

hope this helps