1. main.ts is starting point of angular application
2. main.ts refers to app.module.ts which tells the components to be considered during bootstrap
3. the component by default would be AppComponent which loads the app.component.html
4. index.html is the root html file which loads the whole app in broswer.When you inspect index.html it would have the same code as one in editor showing loading. The JS files would replace the content in index.html once it gets loaded.Its the same js file which gets generated during ng build placed in dist folder
5. All components newly added should be registered in app.module.ts. This file is like registry which would help angular to keep track of components

main.ts -> app.module.ts -> Check for bootstrap component