It's a spectrum, not a graph.
There is a good chapter on this in Organic Chemistry, by Clayden, Greeves, Warren & Wothers. It walks you through it nicely. It's well worth buying this book so you always have it to hand.
For more advanced treatment, check out some of the oxford chemistry primers, Harwood & Claridge - Introduction to organic spectroscopy, Hore - nuclear magnetic resonance (very physical) and Iggo - NMR spectroscopy in inorganic chemistry (for other nuclei, including quadrupolar nuclei)