A Component is a programmable container that holds application and presentation logic. Any element on a web page can be regarded as a component. For Instance a button could be considered as a component.
In Angular, the Entry Level Component is called App Component. A Component normally contains 4 files
The Presentation Logic is written in app.component.html, The Application Logic is written in app.component.ts. Code for styling is present in the app.component.css file and the code for testing resides in the app.component.spec.ts file.
I would be discussing this in further detail in my upcoming blogs.