The question surely refers to Pino - a procedurally generated and moved skeleton figure
three.js provides simple geometry at its core, but for effective use, I created custom geometry to clearly create the body parts and put them in the right position.
The bones are also created using the custom newBone function to achieve the correct positions.
To understand the principle, the previously created example may help.
CustomCylinderAndKnee
However, Pino is not an example to start with as a beginner. It is already quite complex.
One possibility is to remove all bones with associated body parts piece by piece (starting from hands, feet) to better recognize the basic principle.
Usually animated figures are created with software like Blender.
Pino is a test to see to what extent you can do it procedurally. It has its limitations.
I recommend you as a beginner to look at the code of some examples of Collection of examples from discourse.threejs.org. 