Need help understanding ZigZag code

Hey men,
A little update!
Thanks to this wonderful video I've figured out how it is drawing stuff in addition to the way to do it myself.



If you guys have some information on the remainder of my questions I want to know since I've yet to figure that out.

Hey guys,
I was trying to learn more about programming stuff in MQL4 and that I wished to attempt and program a ZigZag indior so I looked at an existent one to learn the best way to code one myself however I'm a little stuck.

Here is the code that I was looking at and that I have some questions.
Https://pastebin.com/hk0BFKx0

-So first of all how can an indior like this work in simple terms?

-I was hoping to publish some stuff to understand more however it did not print a thing even though there were not any errors.
What I was trying to publish was ExtZigzagBuffer[I] during the first while loop but didn't do anything.

-What is extremum and extlevel (Extremum level?) And where does the 3 come from in extlevel = 3?

-How does it draw the lines?
All I could find about drawing material was:
//-- drawing preferences
SetIndexStyle(0,DRAW_SECTION);

I discovered to draw stuff using ObjectCreate.



So if anybody has any advice that might help me know the code along with the rationale behind it let me know and it will be appreciated!

Thanks