The Em shape barre chord on the 1st fret equals Fm (F minor):
You cannot play every chord in the guitar’s open position.
What if you wanted to play an F or B chord? How about an F# or Gb chord for that matter? You can’t do it without using a barred chord. There are 12 possible major chords and without barre chords you can only play 5 of them. It’s the same thing with minor chords. A barre chord is where we take a basic chord pattern and “move” it up the neck of the guitar to create different chords.