Slash Chords

The first time anyone ever comes across a slash chord, he immediately says HUH? Well, they are really not that hard to figure out. Let's look at G/B. It is read B over G. What you do is play a G major chord with a B as the bass note (The B is the lowest note of the chord). The G major chord's notes are G, B, and D. If you look at the diagram of G/B, you will notice that it has all the notes of the G major chord. The only difference is that the B is the lowest note, instead of the G. That is why it is named G/B instead of G.
Chords are written in this way to specify a certain bass note or voicing. Often, the bass notes will be arranged for a specific bass line. Without specifying, most would play a more common G major chord., but G/B forces the guitarist to play B as the lowest note in the chord.
In the examples below I show three slash chords. You will notice that the bass note is always a chord tone of the underlying chord as I explained above.

Now Let's look at an Dadd9/F♯, or Dadd9 over F♯.

Dadd9/F♯

Now, let's look at E♭/B♭, or E♭ over B♭.

E♭/B♭