D3 describe themselves as a framework for data-driven documents. It is really great for visualizations of data, from a simple bar chart to really advanced interactive maps. (link to examples) D3 is, for example, used by Microsoft to create visualizations in PowerBI.
Listen, learn and enjoy.
Charting libraries built on D3:
- C3.js http://c3js.org/
- NVD3 http://nvd3.org/
- dc.js https://dc-js.github.io/dc.js/
- d3.chart http://misoproject.com/d3-chart/
Information about work on D3 version 4:
- Github branch with API links https://github.com/mbostock/d3/tree/4#arrays
- Essay by Mike Bostock on the design of a good API, with examples of changes in D3 version 4
- Introduction to the version 4 module system and how it can be used to create plug-ins
And, of course, the best place to get started:
There are many introductory books available now, some of them online for free, and numerous tutorials. Start simple, understand the basics, and build from there!