Arpeggios are very closely related to scales, actually, arpeggios are part of a scale. Looking at a scale and an arpeggio you can see that an arpeggio is made of the root (or first), the third*, the fifth, and octave (eighth) of the scale. Like the major and minor scales, these arpeggios can be moved all over the neck. This leads into the basics of bass lines that don't just follow the guitar player (that's a good thing). *(the second page explains the importance of the third)