Using rrdtool is not complex. However, there is a learning curve since the round robin database concept is somewhat different to other databases. There are also a lot of options you need to understand. Directly jump into the rrdtool documentation can be hard. That's why I created this list of rrdtool tutorials.

rrdtool tutorial list

http://oss.oetiker.ch/rrdtool/tut/rrdtutorial.en.html
The best tutorial to get an overview what rrd is all about and how to use it.

http://www.generationip.com/documentation/Howto/46-rrdtool-round-robin-d...
This tutorial provides a very easy to understand example. In the beginning of the post, they also explain the rrd-concept with a nice graphic.

https://calomel.org/rrdtool.html
Great examples to get a deeper look on how you can configure rrd. I used the example to get a better understanding about how the rrd graph works.

http://www.phparch.com/2011/02/creating-rrd-graphs-in-php/
A brief overview of how you can create rrdtool graphs with the phpwrapper functions. A short and great overview of how rrdtool works.

http://www.vandenbogaerdt.nl/rrdtool/tutorial/
Alex van den Bogaerdt's tutorial about the rrdtool is actually featured on Oetikers website. But on his website, there is even more information and hints about rrdtool.

rrdtool documentation

http://oss.oetiker.ch/rrdtool/doc/index.en.html
The official rrdtool documentation.