One always learns well from simple examples. The original examples are sometimes quite difficult for beginners to overlook.
In the source code are links to the origin.
A selection of these for the beginning. Note .addAttribute is now better .setAttribute
https://hofk.de/main/discourse.threejs/2017/BufferGeometry/BufferGeometry.html
https://hofk.de/main/discourse.threejs/2017/Indexed%20BufferGeometry/Indexed%20BufferGeometry.html
https://hofk.de/main/discourse.threejs/2018/SurfaceGometry/SurfaceGometry.html
https://hofk.de/main/discourse.threejs/2018/Box%20DatGui/Box%20DatGui.html
https://hofk.de/main/discourse.threejs/2018/Camera-Beginner/Camera-Beginner.html
https://hofk.de/main/discourse.threejs/2019/CameraMovement/CameraMovement.html
https://hofk.de/main/discourse.threejs/2019/MoveObject/MoveObject.html
https://hofk.de/main/discourse.threejs/2018/TweenCubesRotation/TweenCubesRotation.html
https://hofk.de/main/discourse.threejs/2018/connectMeshSprite/connectMeshSprite.html
https://hofk.de/main/discourse.threejs/2018/interactiveShape/interactiveShape.html
https://hofk.de/main/discourse.threejs/2019/WallBuilding/WallBuilding.html
https://hofk.de/main/discourse.threejs/2019/ColorStripeChanging/ColorStripeChanging.html
https://hofk.de/main/discourse.threejs/2020/PlanePoints/PlanePoints.html
Enjoy