What is it
Nivo is a rich set of data visualization components for React applications. It's built on top of D3 and comes with powerful builtin components which abstracting await the complexity of the D3 library. It is also highly customizable data visualization with well-written documentation which enables us to quickly develop charts.
Why we use it
Nivo has a well-written document which includes lots of examples. It removes complexity of building chart components.
When to use it
Whenever you need a chart for displaying or comparing data, your first choice should always be Nivo. If your task is to complex to build with Nivo, you have the option to build it with D3 instead.
How to learn it
The Nivo docs has a lot of examples of the different components available and the possibilities you have customizing them.