You’ll want to create a barre with your first finger except you will not include the low E string. Instead we’re using the A string as our root.
A Major Open
A Major Barred
(audio example is A#/Bb root note on the 1st fret)
You can determine the name of the chord when the root (lowest) note is played on the frets in the chart below.
Here is a poplular alternative way of playing the A style barre chord. It’s the same form with the exception of the missing note on the high E string. It used a lot because it’s an easer fingering than the full barre chord.
Play the A style barre chord on the first 12 frets starting on the 1st fret. Listen to this exercise in the audio example below. You may want to say the names of the chords as you travel up and down the fretboard to help you remember them.