Vst3 host

Hi,
I found the AudioPluginHost and can open it and compile it (Visual Studio 2022).
I want to build a terminal based vst-host. I created a project without a gui and managed to set the basics up.
I created a VST3PluginFormat and called createInstanceFromDescription.

But coming from a beginner c-programmer (and musician) I cannot understand AudioPluginHost_App reads and processes the audio-data.

Here is my code (I cannot upload it because I am a new user)

    juce::ScopedJuceInitialiser_GUI mm;
    //juce::AudioDeviceManager aman;
    
    juce::AudioDeviceManager manager;
    manager.initialiseWithDefaultDevices(2, 2);
    

    //std::cout << manager.getCurrentAudioDeviceType().toRawUTF8() << std::endl;
    juce::PluginDescription desc;
    desc.fileOrIdentifier = "C:\\Program Files\\Common Files\\VST3\\Emissary.vst3";
    desc.pluginFormatName = "VST3";

    juce::VST3PluginFormat format; //AudioPluginFormat
    format.createInstanceFromDescription(desc, 44100, 0);

    juce::AudioPluginFormatManager formatManager;
    juce::AudioProcessorGraph graph;
   
    auto plugin = formatManager.createPluginInstance(desc, 44100, 128, " ");

    graph.addNode(plugin);

#if 0
    formatManager.createPluginInstanceAsync(desc,
    graph.getSampleRate(),
    graph.getBlockSize(),
    [&] (std::unique_ptr<juce::AudioPluginInstance> instance, const juce::String& error)
    {
        //addPluginCallback(std::move(instance), error, pos, useARA);

        if (instance == nullptr)
            exit(-1);

        instance->enableAllBuses();
    });



    juce::AudioSourcePlayer fPlayer;

    fPlayer.setSource(&graph);
    manager.addAudioCallback(&fPlayer);
#endif

Thanks for your help!