Barre chords are a way of “moving” the neck of the guitar to a higher key. Here’s a big giveaway on the secret of a barre chord. Let’s play an ‘A’ chord with an ‘E’ string root. First you need to barre over all 6 strings on the 5th fret, and then play an ‘E’ chord shape. But you hear an ‘A’ chord. Do you see that by moving the neck you are changing the key? In order to play an ‘Am’ chord on the ‘E’ string, you would barre the 5th fret then play an ‘Em’ Shape. Are you getting it yet? Pretend that your “Barring Finger” isn’t even there; it’s just the nut like it always has been. Your Middle, ring and pinkie finger are the only ones playing the actual chord shape.
Can you play an ‘E7’? Now barre over the 3rd fret and play it and… bam! You have a ‘G7’! What about the ‘A’ String root chords? These chords are harder to play and take more practice. The reason they are harder is just this, you have to mute the low AND high ‘E’ strings. You can only hear the middle 4 strings… tough, eh? Well barre over the middle 4 strings and play an ‘A’ chord shape on the 5th string and… bam! You got a ‘D’ chord!
This technique will work on the ‘E’ and ‘A’ strings for ALL chord shapes. Have fun! The rest is up to you to figure out.