The first chord is an A chord, but with a half -barre (flatten your first finger). Taking the top note (A) down one fret gives you A maj7, then A7, then A6.The numbers in chord names refer to intervals - the distance from the starting note, using the notes of the major scale.

So A to A is 8, A to G sharp is 7, A to F sharp is 6, etc. This rule works for all chords.

This pattern could be moved up the fretboard - for instance if all the chords were moved up 3 frets we'd be in the key of C, and the chords would then be C, Cmaj7, C7, C6.

Next the same idea is transferred to a root 5 shape - now it's the middle note (A) that's moving.

Then we have some common chords in this key (complete list is on the left hand column)

We can improvise in the key of A with the scale shown ( both in tab and as a fretboard map) It's also referred to as F sharp minor pentatonic, it's the same notes either way.

Then I've put in the flat 5 or blues notes, which works well for country/blues/rockabilly material.

All this material will work well together in terms of songwriting. A is a favourite key for The Beatles, country, country rock songs.