A Circuit with a Pullup Resistor
One of the things that really confused me, though, was the use of 10kohm resistor with the push button. The circuit looked like this:
5V -- 10,000ohm resistor -- input pin -- push button --GND
It turns out that this is pretty simple. When the push button is closed, you get the circuit:
input pin -- push button -- GND
Which sends no power to the input pin. This is a LOW signal.
When the push button is open you get the circuit
5V -- 10,000ohm resistor -- input pin
And so you are sending power to the input pin. This is a HIGH signal.
So now you can use these values of LOW and HIGH to program button behaviors. Here is a much more thorough explanation on the Sparkfun website. Awesome!