what are guitar chords or scale??

In music, a guitar chord is a chord, or collection of notes usually sounded together at once, played on a guitar. It can be composed of notes played on adjacent or separate strings or all the strings together. Chord voicings designed for the guitar can be optimized for many different purposes and playing styles.
The guitar is generally very capable and versatile for chording purposes, but it does exhibit some differences from other instruments. For a six string guitar in the very largest chord-voicings it may be necessary to drop or omit one or more tones from the chord; this is typically the root or fifth. The layout of notes on the fretboard sometimes demands that the notes in a chord will not run in tonal order. It can make a possible chord which is composed of more than one note of exactly the same pitch. Many chords can be played with the same notes in more than one place on the fretboard.
Guitars can vary both in the number of strings and in tuning. Most guitars used in popular music have six strings and are tuned (from the lowest pitched string to the highest): E-A-D-G-B-E. The internal intervals present among adjacent strings in this tuning can be written 5-5-5-4-5 (with perfect fourth intervals except for one major third interval between the G and the B). Conventionally, the string with the highest pitch (the thinnest) is called the first string, and the string having the lowest pitch is called the sixth.

Six-string guitars with standard tuning

Guitar chords take advantage of the intervals between the strings, which in each case are perfect fourths excepting the interval between the B (second) and G (third) strings, which is a major third. One common non-standard tuning, found in hard rock and heavy metal music, is called drop-D tuning. This requires the player to change the low E string tuning to that of a D note. This tuning allows power chords (see below) to be played relatively easily on the bottom three strings, as the strings are now tuned to a root-fifth-octave (D-A-D) tuning. Many other forms of guitar tunings exist as well.

CAGED major chords

CAGED is an acronym for the five easiest major chords to play.

Major chords contain a root note, a major third above the root and a perfect fifth above the root.
In the case of C Major, these notes are C, E and G. The graphical representation on the left shows how left-hand fingering produces:

• E on the first string
• C on the second string
• G on the third string
• E on the fourth string
• C on the fifth string
• Sixth string not played

In a similar way, the chords A Major, G Major, E Major and D Major are often played as:

• 

  A Major Chord
  
• 

  D Major Chord
  
• 

  E Major Chord
  
• 

  G Major Chord
  

These five chords are fundamental to guitar for a variety of reasons including:

• they are all major triads, and as such they are all primary reference chords
• they all occur and are available in open position (see also Voicing (music) and open chord): the first three frets plus open strings
• their overall gross large shapes become the basis of the CAGED system
• they can be connected and linked together to create one large long contiguous 12-fret or one-octave greater resource pattern of major triad tones encompassing the entire fretboard.

B major and F major shapes

The two remaining whole tone major chords (to complete an octave) are those of B major and F major. These are commonly played as barre chords, with the first finger used to press down multiple strings across the guitar fingerboard.

• 

  B Major Chord
  
• 

  F Major Chord
  

On examination, it becomes clear that these two chords are logical extensions of the A major and E major chords above. The B major chord is the same shape as the A major chord but it is located two frets further up the fretboard. The F major chord is the same shape as E major but it is located one fret further up the fretboard. In effect, barre chords act as if the whole guitar has been shortened, like a moveable nut or capo.
Barre chords in the shape of A and E major can be played anywhere on the fretboard. Wherever they are played, these chords are major because they have the same shape, and this determines the intervals between the notes. The root of the chord in any position can be worked out from the diagrams above.

C major, G major and D major shapes

The other three shapes in the CAGED system are C major, G major and D major. These can be transformed into barre chords in a similar way to the A major and E major shapes.
The CAGED system therefore creates five major barre chords which can be used to play all the major chords in more than one position on the fretboard.

• 

  The C major shape on the fourth fret becomes E major
  
• 

  The G major shape on the second fret becomes A major
  
• 

  The D major shape on the third fret becomes F major
  

Other CAGED chords

The CAGED system can be modified to produce many other chords, only some of which can be covered here.
These require the basic shape of the chord to be modified so that it has slightly different intervals between each note. Once this is done, the shape can be played anywhere on the fretboard, as above.

Minor, Augmented and Diminished

Minor chords (commonly notated as C-, Cm, Cmi or Cmin) are the same as major chords except that they have a minor third instead of a major third. This is a difference of one semitone.
To create F minor from the F major chord (in E major shape), the second finger should be lifted so that the third string plays onto the barre. Compare the F major to F minor:

• 

  F Major Chord
  
• 

  F Minor Chord
  

The other shapes can be modified as well:

Chord name	Fret numbers
E minor	[0 2 2 0 0 0]
A minor	[X 0 2 2 1 0]
D minor	[X X 0 2 3 1]

The C major and G major shapes cannot be modified in this way because the major third in those shapes falls on the bar (or nut). It is therefore impossible to lower that note by one semitone (to produce the minor third) and retain the barre. C minor and G minor therefore have to be played using one of the other CAGED shapes.
Augmented chords (major third and augmented fifth) and diminished chords (minor third and diminished fifth) can be created in much the same way.