A Temporary Capo

A barre chord is simply a guitar chord where one finger (usually the index finger), frets more than one string at the same time. Many times the index finger frets all strings in one fret and acts as a “temporary capo”.  

F chord

This is how we would chart an F barre chord. Notice the curved line demonstrating that this is a barre chord.

This is what an actual F barre chord looks like on the guitar.  Notice the fairly straight line from point of index finger to the knuckle.  Also, the wrist is below the neck of the guitar, not behind it.