Barre chords (or bar chords) require one finger to fret most or all of the strings to play the guitar chord.
The index finger is used to do this and enables the chord to be moved up and down the neck.
The diagrams below show how to play major and minor barre chords in standard tuning. The curved lines shown in the diagrams indicate the notes that are barred (fretted using one finger).
Major Barre Chord Forms
Root notes on 6th and 5th Strings
Guitar Tab example of a chord progression using Major Barre Chords
G C D e|-3--3--3--3--3--3--3--3--5--5--5--5--5--5--5--5-| B|-3--3--3--3--5--5--5--5--7--7--7--7--7--7--7--7-| G|-4--4--4--4--5--5--5--5--7--7--7--7--7--7--7--7-| D|-5--5--5--5--5--5--5--5--7--7--7--7--7--7--7--7-| A|-5--5--5--5--3--3--3--3--5--5--5--5--5--5--5--5-| E|-3--3--3--3-------------------------------------|-->
Minor Barre Chord Forms
Root notes on 6th and 5th Strings
The guitar tab below is a similar chord progression with a minor barre chord (Em) included. Notice how the use of minor chords give progressions a different sound and feel.
G C Em D e|-3--3--3--3--3--3--3--3--7--7--7--7--5--5--5--5-| B|-3--3--3--3--5--5--5--5--8--8--8--8--7--7--7--7-| G|-4--4--4--4--5--5--5--5--9--9--9--9--7--7--7--7-| D|-5--5--5--5--5--5--5--5--9--9--9--9--7--7--7--7-| A|-5--5--5--5--3--3--3--3--7--7--7--7--5--5--5--5-| E|-3--3--3--3-------------------------------------|