In music, a guitar chord is a set of notes played on a guitar. A chord's notes are often played simultaneously, but they can be played sequentially in an arpeggio. The implementation of guitar chords depends on the guitar tuning. Most guitars used in popular music have six strings with the "standard" tuning of the Spanish classical-guitar, namely E-A-D-G-B-E' (from the lowest pitched string to the highest); in standard tuning, the intervals present among adjacent strings are perfect fourths except for the major third (G,B). Standard tuning requires four chord-shapes for the major triads.
In major-thirds tuning, the interval between open strings is always a major third. Consequently, four frets suffice to play the chromatic scale. Chord inversion is especially simple in major-thirds tuning. Chords are inverted simply by raising one or two notes by three strings. The raised notes are played with the same finger as the original notes. In contrast, in standard tuning, the shape of inversions depends on the involvement of the irregular major-third.
Russell, George (2001) . "Chapter 1 The Lydian scale: The seminal source of the principal of tonal gravity". George Russell's Lydian chromatic concept of tonal organization. Volume One: The art and science of tonal gravity (Fourth (Second printing, corrected, 2008) ed.). Brookline, Massachusetts: Concept Publishing Company. pp. 1–9. ISBN 0-9703739-0-2.
With just a little more music theory, you can learn to write simple songs with the chords you've just learned. The song would be in the key of C major (C, D, E, F, G, A and B). You can use the major chords for the I, IV and V notes and the minors for the II, III and VI notes. That means you can play a chord progression which uses all of the chords you've learnt, if you want to.
There really isn't a best age for kids to start guitar lessons, but most children under the age of 7 generally don't have the dexterity or patience needed to learn to play the guitar. With persistence and motivation some kids have learned to play guitar at some impressively young ages, but it really comes down to is the individual attitude and maturity level of the student.
The main purpose of the bridge on an acoustic guitar is to transfer the vibration from the strings to the soundboard, which vibrates the air inside of the guitar, thereby amplifying the sound produced by the strings. On all electric, acoustic and original guitars, the bridge holds the strings in place on the body. There are many varied bridge designs. There may be some mechanism for raising or lowering the bridge saddles to adjust the distance between the strings and the fretboard (action), or fine-tuning the intonation of the instrument. Some are spring-loaded and feature a "whammy bar", a removable arm that lets the player modulate the pitch by changing the tension on the strings. The whammy bar is sometimes also called a "tremolo bar". (The effect of rapidly changing pitch is properly called "vibrato". See Tremolo for further discussion of this term.) Some bridges also allow for alternate tunings at the touch of a button.