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
The best tutorial to get an overview what rrd is all about and how to use it.
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.
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.
A brief overview of how you can create rrdtool graphs with the phpwrapper functions. A short and great overview of how rrdtool works.
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.
The official rrdtool documentation.