There are only a few chords we can play with open strings. If you’ve been playing your favorite band's music while following the lessons, you’ve probably run into some chord shapes that use your index finger to fret 4 or more strings at the same time, or "bar" a fret. Chords like F, Bb, Ab, and Db are chords that are commonly played as barre chords. You can call them barre or just bar chords, but regardless of what you call them, you will have to play them in your musical career.
Why Barre Chords?
Barre chords are used so that common chord shapes can be used to play chords like Ab, F and others that don’t include the notes of the open strings, E, A, D, G, B, and E. Take the Fmaj chord, for example. Since Fmaj does not include any notes of the open strings, we have to temporarily "retune" the guitar by laying our index finger across all of the strings, almost like using a capo. Now, when we play the strings open, we have the notes F, Bb, Eb, Ab, C, and F again on the high E string. Now we can take the Emaj chord shape and play it with our remaining fingers in respect to our index finger. You can also think of barring a chord as using your index finger as a capo, and then playing the regular open chord shapes. Now let’s look at some common shapes
These two shapes are major shapes. Make sure to note where the root note is in each. The lowest note is the name of the chord. The Fmaj shape is movable up and down the neck but not across strings. If the root note is on the low E string, then you will use the Fmaj shape above. However, if the root note is on the A string, you will use the Bmaj shape above. It is very important that you play the correct shape, or you are simply playing the wrong chord.
These are minor shapes. Like the major shapes they, must be played a certain way depending on where the root note is. If the root note is played on the E string, play the minor barre chord like the Fm. If the root note is on the A string, play the shape like the Dm.
These are 7th shapes. They are major chords with an added note. The added note is the flat 7th of the major scale. These are popular shapes in funk and jazz. Make sure you know these, and, like any barre chord, make sure you know what shape to use judging by what string the root note is on.