Here is an updated prototype for online lessons / exploration tools. This is based on earlier prototypes that I created as part of my Capstone Project at Marlboro Grad Center. This one has a tabbed interface, to allow for additional information: lesson description, result note information, instructions (help), audio help, lesson index and web links.
This page allows you to explore intervals, or the distances between notes (# frets) and how they sound together and how well they harmonize. Choose an Interval by clicking one of the 13 radio buttons (0-12). Each Interval has a name, and sometimes an alias name (for example A4=d5 means augmented 4th = diminished 5th). Each Interval also has a Half-Step count, which basically is just counting frets between notes. Zero (0) half-steps is Unison or P1, or the same note. The distance of 12 half-steps (equals 12 frets) is one full octave (P8), and is like playing an open string, and then at the 12th fret for the same string. For the octave case, the note names would be the same.
Intervals are related to Scales and Chords. For Scales and Chords, there is a Root Note, and then other notes that are related. These other notes have an Interval distance or relationship to the Root Note. For example, if the Root Note is A, and the Interval is m3 (minor 3rd = 3 frets), then the other note is a C. The A+C note pair appears in an A minor scale (A-b-C-d-e-f-g-a) and also in the A minor chord (A-C-e).
You have two choices for note (dot) colors, one for the Root Note and the other for the related note by Interval. This is intended to help you visualize where the notes are and the fretboard fingerings.
You can also click on the notes, or click the Downstroke / Upstroke buttons, or the Play buttons on Note Info tab. This will allow you to hear the note pairs and learn how each Interval sounds (how well it harmonizes).