Good point. They are all example data. The "[[3,6],[6,9],[12,18]]" can be thought of as the coordinates of a comet, and 2 is your predicted correlation, the slope, followed by 1 your predicted constant, the y-intercept. In this case, you want to change 2 and 1 to find the combination that results in the lowest error. It the same with "Error = 4^2 + (-1)^2 + 6^2", it's an example of an error function. Does that make sense?