D3 has some fairly extensive API documentation on GitHub, which I personally believe is pretty great. There are also links to various resources on d3 GitHub wik

D3 has some fairly extensive API documentation on GitHub, which I personally believe is pretty great. There are also links to various resources on d3 GitHub wiki and for extra measure I personally like to study Michael Bostocks' bl.ocks.org site for example visualization a with code samples. Nothing beats thousands of example implementations written by the creator of d3 himself.