Why are there 2 different chord charts for Ab on the chord builder?
Please explain when it's better to use 1 as opposed to the other.

Thanks In Advance,
Uni

Are you talking about this? http://www.8notes.com/piano_chord_chart/Ab.asp

In which case these are two Ab Major chords. The first one is a simple Ab Major triad in root position (meaning that the Ab is in lowest voice. The second option is still an Ab Major triad, but now in first inversion (meaning that the 3rd of the chord, C, is in the lowest voice). The third option that isn't shown is second inversion (meaning that the 5th of the chord, Eb, is in the lowest voice).

The function of inversions (root, first, and second) has it's roots from figured bass and contrapuntal voice-leading. The easiest way to think of it is that the root is the most stable chord, the first inversion is less stable, and the second inversion the least stable (used often to create a "passing note" in the bass voice). Inversions also serve to create different voice leadings in tonal harmony.