Angular is build up on components.
The starting poing of an Angular app is the bootstrapping of the initial component. Angular runs on a component-tree model. After the first component is loaded it will look in that component HTML view and verifies if it has any nested components. If yes, Angular will find matches and will run the corresponded code.
A component in Angular is used to render a portion of HTML and provide functionality to that portion. It uses a component class where the application logic is added.
For every component in Angular you can specify an HTML template. Angular provides template syntax to wire the templates to DOM events.