NgModules

The basic building blocks of an Angular application are NgModules
NgModules which provide a compilation context for components.
NgModules associate related code into functional sets.
An Angular app is defined by a set of NgModules.
An app always has at least a root module that enables bootstrapping that launches the application.
NgModules can import functionality from other NgModules, and allow their own functionality to be exported and used by other NgModules.

NgModules are containers for a cohesive block of code dedicated to an application domain.

They can contain components, service providers, and other code files whose scope is defined by the containing NgModule.
They can import functionality that is exported from other NgModules,
They export selected functionality for use by other NgModules.
Every Angular app has at least one NgModule class,
The root module, which is conventionally named AppModule and resides in a file named app.module.ts. You launch your app by bootstrapping the root NgModule.