Basics of Sharepoint Framework Webparts

This post is intended to share my knowledge on basics of sharepoint framework webparts.
Below are the tasks we address:

1. Why sharepoint framework (SPFx).
2. How to setup a machine for it
3. How to develop your first SPFx webpart
4. How to deploy it to your SPO.
5. How to Consume it on client SPO site.
6. How to upgrade your SPFx app/webpart.