Скачать или смотреть Arm Model Development in OpenColab (OpenSim in Colab)

Simple Arm model Building in Colab using OpenSim API
Pardis, our explorer, learned how to perform scaling a generic model in OpenSim using Colab. It was great since she saw the changes in the model from the size of the model. She then thought: well I can do this, but how the model was developed?
The aim is to simulate the following, however, OpenColab visualization still is working in progress so we do the scripting here only for now (the animation comes from OpenSim GitHub):

I need to learn the details of it like
What is a muscle (or actuator)?
What is joint? What type of joints do we have?
What are constraints, marker sets, Controllers, and even Probes?
How can I learn them? I need a simple model to easily explore its details.