In this day and age the joy of Google is knowing the exact technical term to use in a search. I am assuming that your referring to the Chapter “Timestamps” on YouTube videos. This was asked recently on the forum and it was reported that it is done by hand. You can see the thread here:
Additionally, here is a fairly recent article explaining the process:
which was found in duckduckgo with:
embed timestamp chapter video
If you are looking for something else or have additional questions, just ask.