I'm a guitar teacher and part-time college lecturer. As a result of many years of teaching guitar I can save you some time.

In the chord pictures below I've tried to identify the essential chords, and these are probably the most used across all forms of popular music.

Chords in the key of C : C Dm Em F G7 Am (and Bm7b5)

Most songs will use these chords in combination, so it makes sense to learn them together.

C F G7 are the major chords, Am Em and Dm are the minor chords.

Work on changing from C to Am (called the relative minor) and then changing from C to F. In both cases finger 1 stays down on the fretboard, and don't play string 6, the thickest string.

NB: Chord grids - the 6 vertical lines are the strings, the horizontal lines are the frets.

Chords in D: D, Em, F#m, G, A7, Bm, C#m7b5.

Most simple songs will use D G A7, plus Em and Bm sometimes. Most Dylan songs, especially the early ones can be played with a very limited choice of chords.

As Bm is a barre chord it can present problems for the beginner. Check out my solution - Bm7. Just play the middle 4 strings and this will work well, and be quite easy to change to. A fix for F#m is to play fret 2 on strings 6,4,3, leaving string 5 (A) open. Ideally, mute this string by slanting your first finger over a bit.

Generally, the lowest note or bass note of a chord wants to be the same as the name of the chord. So Am has an open 5th (A) at the bottom and you don't play string 6 (E). Same applies to A and A7, or any variant of A such as A maj7.

In a similar way, D has open D (string 4) at the bottom, don't play strings 6 and 5.

C, or any of the variants such as C7 - don't play string 6. You want a C at the bottom of the chord, fret 3 on string 5. Having a low 6th buzzing away is probably the most common beginner mistake, but one that is very easy to fix!

When you can put this into practice it will really make things sound better, and clearer.

The guitar is tuned (low to high, thickest to thinnest string) E A D G B E.

Look at A7. It's just the same as A, with the middle note removed.

Look at E7. It's just the same as E with the middle note removed.

The 7 note actually means flat 7th, in musical code. In C: CDEFGABC is the major scale.

Count down from high C, note 8

B= maj 7th

Bb= 7th

A=6th.

So C maj 7 is CEG (the notes in a C chord) plus B

C7 is CEG plus Bb

C6= CEG plus A

Now let's look at D chords. Starting with common-or-garden D, if you move down the middle note in half-steps,or one fret at at time, we get D maj7, D7 - all strongly related chords.

Now try doing the same thing with an A chord. Moving the middle note down one gives you Amaj7, then moving down again gives you A7.

Very commonly a 7th chord, also known as dominant 7th, resolves to the tonic or home chord in any key. So practice going from A7 to D, G7 to C, B7 to E and you will be doing some useful preparation for learning songs quickly and easily. If you really concentrate on this it will help in ear-training, which might well happen anyway without any effort.

Most simple songs, by which I mean folk,blues,nursery rhymes,most 1950s-era pop songs will use just three chords, which are chords 1,4,5 from the harmonised scale sequence. In the key of C these would be C, F, G7.

in the key of D: D, G, A7

in the key of G: G, C, D7

These are the basic building blocks used to create a song. Sometimes one of the minor chords is also used, often the relative minor - Am in the key of C. So a typical doo-wop Why must I be a Teenager? -type lament might go

C Am F G7 - endlessly!

If you play these chords in different keys you'll see that the sound is the same, the chord relationships and distances are the same too. It's only the pitch that has changed.

My new hub Guitar-advanced and jazz has info on more interesting chords, and pictures of the most important types.

My new hub Guitar- easy blues has chord pictures and chord charts, and will probably help with this section.

Blues is a form of music based on 7th chords. So a typical easy 12-bar sequence would go:

E7 (x4) A7 (x2) E7 (x2) B7 A7 E7 B7. Play each chord four times.

Once this is sounding good, you could substitute 9th or 13th chords for any of the 7ths and it will sound more jazz or funky.

It's worth noting that early rock n'roll and rockabilly is basically a speeded-up version of the 12-bar blues - so most Chuck Berry, Eddie Cochran, Elvis songs from this era are just variations on a theme. A good theme though.

Learning the blues chords will enable you to play literally hundreds of songs like Blue Suede Shoes, Houndog, Sweet Little Sixteen, Johnny B Goode.

Playing in other keys: try using a capo. For instance, in fret 1 this would put you in the key of F, beloved by sax players, fret 3 would be G, fret 5 would be A. If you're singing, it might help you find a more comfortable key to play a song in. Personally, I'll always try out a few different keys until I find one that sounds good.