Need help for a basic coding to make extension

Thanks for the answer.
As you said Endoscopy module is a nice example to study.
And the github link is also very helpful.

Would you mind if i ask some more…
Scripts of some modules like endoscopy are shown in the link but many built-in modules like Volume rendering, Segmentation or Markups are not given as scripts but as a more complicated way…

If it’s very easy for you, could you tell me what should I do, for example, to take volume rendering into my own extension?