Architecture overview

The fundamental building blocks of an Angular apps are NgModules.
NgModules provides a compilation context for components. 
NgModules collect related code into functional sets.
Angular app is structured by a set of NgModules. 
An app always has at least a root module that enables bootstrapping of app, 
and typically it has many more feature modules.

Mainly Angular App consist of followings:

• NgModules
• Components
• Template
• Services
• Routing
• Depedency Injections

Ref: angular.io