Barre chords are the opposite of open chords since there are no open strings or un-fretted strings in a Barre Chord. One usually places the index finger over the whole fret/neck barring the neck and then arranges the other fingers in a certain shape to form the chord.
In this video I beginn by showing the correct barring posture as well as the typical Barr shapes people learn at the earliest stages: F major, F minor where the root is on Low E-string, and B major and B minor where the root is located on the A-string. Remember these shapes can move up and down the neck horizontally to change the key or root note of the chord which in turn defines the name of the Chord. For more info on these Barre Chords check out the Triad Chords page in Music theory.