I would start with an fairly recent tutorial written by Bostock himself:
https://observablehq.com/@d3/learn-d3A point I personally needed to grasp back when I first worked with D3 was that the data drives the visuals (hence data-driven documents). It was not an animation library. It's also not a charting library, but some charting libraries are built on top of D3.
Lastly, the D3 wiki also contains links to other tutorials, but they're most likely running on v3:
https://github.com/d3/d3/wiki/Tutorials