Below are the major components of Angular 2
Modules − This is used to break up the application into logical pieces of code. Each piece of code or module is designed to perform a single task.
Component − This can be used to bring the modules together.
Templates − This is used to define the views of an Angular JS application.
Metadata − This can be used to add more data to an Angular JS class.
Service − This is used to create components which can be shared across the entire application.
This blog is very nice.Components are the most basic UI building block of an Angular app. An Angular app contains a tree of Angular components. Angular components are a subset of directives, always associated with a template selenium tutorial for update knowledge on selenium.