If you play a regular open Cmajor and play the Ab on the 1st fret of the G string it's an C augmented chord. You should substitute the G for the Ab though. If you play the Ab on the 4th fret of the Low E string as well as playing the open C major chord it becomes a G#major7+5
Phil is correct.
Use the Ab augmented as a passing or transition cord between Ab major and Db major to give you an idea how it sounds and resolves itself . Move from Db major to Ab major using Ab diminished [first 4 strings: Ab, D,B,F] in between to hear a different transition. Just one example, but your ear should hear the difference. You'll find a lot of ways to use the chords in different keys and positions. Listen to the harmony's. Very basic, but very cool. I'm sure there are a lot of guys here that can offer their own suggestions or alternatives.
Hope this helps.
PS click on the link below to see how the avatar should look. http://www.vhfans.com/boards/userimages/1998.gif
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