Chords are based on harmony, using every second note in a dominant scale, starting with the root note. The dominant scale is the same as the major scale, except the 7th note which is a semitone flatter.

GuitarSite.com has links to a vast range of chord resources at:
www.GuitarSite.com/chords.htm and includes chord info, such as:

WHAT IS A BARRE CHORD?

A barre chord takes its name from the role of the 1st finger of your left hand. This finger acts as a "bar" across the fingerboard, depressing all six strings and replacing the nut (the ivory piece at the top of the neck). By using your first finger as a "bar," you can move many of the open chords you have learned up and down on the fingerboard.

WHAT IS A POWER CHORD?

A powerchord is a chord which contains no 3rd (suspended chords, and chords containing 3 or more notes exempted). Technically, a powerchord is not really a true "chord" because, by definition, a "chord" has to have a minumum of 3 notes. Powerchords are also called "5" chords, notated as C 5.

Chords - The Theory - continues at:
www.GuitarSite.com/chords3.htm And covers: Intervals, Seventh, naming, Triads, Inversions, Voicings, Alternate names for chords, Polychords, Powerchords, Slash Chords

Want to learn chords without reading music? Read this:
www.GuitarSite.com/chords2.htm

There is a guitar chord game at:
www.GuitarSite.com/game.htm

The melodic minor scale and the dominant seventh flat9 (V7b9) chord (!) are covered here:
www.GuitarSite.com/chords4.htm

You will find heaps of other great chord resources reviewed at:
www.GuitarSite.com/chords.htm#ChordLinks

Other sites include Guitar.com, which has a dynamic chord generator that shows you how to construct almost any chord on the fretboard at www.guitar.com/chordgen

Or Chord House: Scroll easily through more than a thousand guitar chords and immediately see what notes they consist of and how to play them on your guitar. Now also includes augmented and diminished chords www.looknohands.com/chordhouse

For chord notation of individual songs, look at tablature:

GNW article: Where to get tablature:
www.GuitarSite.com/newsletters/990621/2.shtml

Tab resources at GuitarSite.com
www.GuitarSite.com/contents.htm#tab
www.GuitarSite.com/tab.htm

The 2000 Guitars Database has new entries daily:
www.GuitarSite.com/database/Tablature