Example needs more explanations

Hey,
I'm new to OpenCV and the examples are very helpful but there are things that I can't feature out.
I think adding an explanation of what an example do and a small comment on each line/function will be match help to me and others that just beginning with OpenCV.

Thanks
Tzelon

Review the repository's examples to identify which examples lack explanations and comments. Document what each example does and add concise comments for its lines or functions; done means the examples are understandable to beginners, though the issue does not specify particular files or examples.

Written by the indexing model from the issue text.