Learning to tune a guitar is an essential skill to master. Your playing will never sound as good as you hope if your instrument is not in tune. You can of course use an electronic tuner but the ability to tune by ear will greatly improve your musicianship.
Note: Normal tuning is as below
Pitch
A guitar can be tuned so that all strings are tuned to one another, however if you want to play along with a recording or maybe even in a band, you'll need to tune to the correct pitch. Tuning forks have traditionally been used to tune the E or A string to the correct pitch. A piano or keyboard or another in-tune guitar could be used instead.
The open strings from the lowest (thickest) string to the highest (thinnest) should be tuned as detailed below:
Tuning at the 5th fret
Once you have tuned the lowest (6th) string to E, this can then be used as the starting point to tune all other strings.
1. Play the note on the 5th fret of the lowest (6th) string you've already tuned. This produces an A note.
Next, whilst plucking the 5th string, turn its machine head (tuning peg) until the pitch of this string matches that of the 6th string you're fretting.
If the open 5th string sounds a little higher than the fretted 6th string, turn the machine head to slacken the string. If, however, it sounds too low, tighten it. You've now tuned the 5th string to A.
2. You can now play a D note by picking the A string at the 5th fret. The open 4th string (the next thickest string) can now be tuned to the fretted A string in the same way. This method can also be used to tune the G string.
3. The system changes when you get to the B string (2nd string). This string needs tuning to the pitch of the note on the 4th fret of the G string.
Once this B string is in tune, fretting it at the 5th fret will produce the E note which can be used to tune the open 1st string.
Barre chords (pronounced "bar chords") involve using the first finger to fret across all 6 strings with the remaining fingers shaping the chord. This shape can then be moved up and down the fret board, creating whole new chords without having to reposition your fingers much, if at all.
Using barre chords also allows you to create otherwise unattainable chords such as Bb minor or F# major.
Playing major barre chords
Start with a normal open position E major chord but use the 2nd, 3rd and 4th fingers. Move this shape up and down the fret board using your first finger to fret all strings on the adjacent lower fret to create different chords.(DIAGRAM))
> G major barre chord based on an E major shape played at the 3rd fret. Move this to the 5th fret for A major and to the 7th fret for B major.
Most guitars will have a marker on frets 2,5 and 7. Moving your E major barre to these positions will give you the chords of G, A and B major.
5 tips to improve Barre chord technique
1. Keep your 1st finger straight and in line with the fret.
2. The creases in the joints of your fingers should not coincide with strings.
3. Position your fretting fingers as close to the fretwire as possible.
4. Press down firmly but do not use excessive pressure.
5. Practice, practice, practice.....
In theory, you could use this barre chord shape to play all major chords but in practice you'd be darting up and down the fret board far too much during a song.
Knowing at least 2 shapes for each chord will allow you to play most songs within the space of only a few frets.
The second major shape that can be converted to a barre in the open position is A major. Moving this shape to the 3rd, 5th and 7th frets will give you chords C, D and E. 
> C major barre chord based on an A major shape played at the 3rd fret. Move this shape to the 5th fret for D major and the 7th fret for E major.
Playing minor barre chords
E minor and A minor open position chords can all be refingered to allow the 1st finger to barre.
> G minor barre chord based on an E minor shape played at the 3rd fret. Move shape to the 5th fret for A minor and the 7th fret for B minor.
Mixing major and minor chords
Most songs will contain a blend of both major and minor chords. Now you know major and minor chords in both open and barre positions, you can choose the shapes that will mean avoiding large movements along the fret board.
