Adafruit WebIDE
If you're looking for the best place to start tinkering with a RaspberryPi (RPi) or BeagleBone (BB), I would highly recommend Adafruit's WebIDE. As the names suggests -- it's a web-based IDE, and facilitates physical programming (for RPi -- manipulating the GPIO) on your device.
The installation steps are clearly laid-out, and mostly smooth (for RPi I remember having to take care of a few easy-to-fix issues). Once it's up and running -- it's a delight to work with!
Here's a big shout of "Thanks" to Adafruit!