What are all the components on that aesthetically pleasing blue Arduino circuit board? What does GND stand for, and what is with the "~" mark next to those plastic lifted holes mean?

This tutorial covers the hardware on the Arduino board that you will likely use as you work on projects. It is by no means a comprehensive study of the physical layout, but enough to make you familiar with the parts you will be using.

On an aside - isn't the packaging great too? Clean, compact and appealing - overall fun to open.