Ah, so you weren't saying you thought the JeeNode was harder than the Arduino? Sorry, I misunderstood. I thought you must have had experience with the Arduino board before purchasing a JeeNode, which I think is how most of us got here.
Well there are books for Arduino, but if you're playing with a JeeNode then you might find it frustrating as the pins are all in different places (but all there).
As you surmised, the language is based on C (actually C++), and it's not too hard to pick up.
Have a look at this online (aka free!) tutorial http://www.ladyada.net/learn/arduino/lesson2.html
It's written for the Arduino, so isn't using any of JC's cool libraries, and it's using the Arduino's pin naming scheme, but the ATmega chip is the same, so anything written for the Arduino can be done on the JeeNode. They are 100% software compatible.
This picture will help you translate the pin numbering:
So the example code uses digital pin 13... Check the picture, that's Pin 19 on the ATmega chip, which is connected to the ISP header on the Jeenode... Damn, not so useful, it's not wired to a port (it's in the 2x4 group of holes behind the ATmega chip). You could solder a wire to it, but we don't really need to, it's easier to change software than hardware after all.
Just find the number for one that is wired to a port you want to use. Let's use the digital pin of port 1 on the JeeNode... Check the picture, JeeNode Port 1 Digital (JP1D as it's labelled in the diagram) is pin 6 on the ATmega chip and referred to as Digital 4 in the Arduino environment. There you go, just change:
int ledPin = 13;
int ledPin = 4;
Right, now you know what pin you are controlling, you can either connect an LED across here to ground (with a current limiting resistor), or just use a multimeter to see the effect.
Everything else in that tutorial is fine, the only difference in the digital pin numbering. The tutorial explains the steps, what each line does.
Hopefully this will help you get going.