I've been learning new things on the guitar this summer and thought I'd post about them.
Barre Chords, sometimes called Bar Chords, allow you to move the same Chord "shape" up the guitar to another fret and form a new chord.
Keep in mind that each Fret is a half step. So, good examples are that the E chord, moved up 1 fret (you need to bar the 1st fret then to do the equivalent of moving up the Nut, the place where the strings go over the top part of the guitar neck) forms the F chord! (Because in half steps, the scale is A, A#, B, C, C#,D, D#, E, F, F#,G, G#, ...)
If you move it up 2 frets from the Nut, it would be the F# chord.
Also, the A chord, moved up 2 frets becomes the B chord!
The guitarforbeginners website shows what I'm explaining with a little animation.
I also learned how to easily form Minor Chords from the E and A chords.
When the highest string (the highest frequency, the one closest to the floor) being held down is moved down one fret towards the Nut, a half step (to the minor 3rd), the chord becomes a Minor chord.
So, if you take the A chord and move your finger on the B string one fret lower (toward the Nut) you'll have an A minor chord.
For the E chord, you move your finger on the G string (actually playing a G#) down a half step (1 fret) which in this case is the nut (or an "open" string) to get Em (E minor)!
Am7 and Em7:
To get these minor chords to be minor 7th chords, just remove the 2nd finger (counting from the side of the neck furthest from the floor) so an open string is played.
So, to change the Am to Am7, lift your finger on the G string.
To change the Em to Em7, lift your finger on the D string (you'll only have one finger left, it will be on the A string 2nd fret (playing a B)
The same is true for the A7 and E7 chords.
If you look at some chord diagrams, you'll see what I'm talking about.