To access Chapter Editor, go to the Video Details page for your video and scroll to the 'Add Chapters' section just past your video description:
The video will start playing from the beginning, and an initial chapter will be created at the 0:00 point of the video. This is required for Chapters to be present in your description.
Use the video player and/or the corresponding timestamps to create new chapters at the points in the video where you would like. You can add chapters by clicking on the 'ADD CHAPTER' button at the top-right-hand corner of the screen, and then you can label them and edit their timing below.
YouTube has several requirements for chapters:
1. They must start with an intro at the 0:00 mark
2. You must have a minimum of three chapters in your video
3. Each chapter must be at least 10 seconds long
4. All chapters must have a title
Chapters are individually indexed by Google, which means each section of your video can appear in search results, boosting your chances of being discovered. They also help keep viewers engaged by making it easier to navigate to the parts of your video most relevant to them.