Hi myputer, I had a feeling you were using a PC. Unfortunately, Apple no longer supports Quicktime on a Windows PC. Instead, you need need to use the Movies & TV app that is included with Windows.. However, this will only allow you to play and view the video, not use and see the chapters.
If you want to see and use chapters on a Windows machine I suggest you download the free VLC player for Windows. Otherwise, you would need to use Quicktime on a MAC.