First, hold the guitar. Make sure that you palm is swiftly resting right underneath the neck with your thumb gripping the guitar firmly. Your pinky finger, ring finger and middle finger are the three fingers which will be used in order to play this major chord.
First, put the pinky finger on the second fret of the second last string. In musical terms you must hold down the B string and hold its C# note. Many people would get confused about this note, but the second fret is the easiest way to hold down this note and play A major chord.
After this your ringer finger will come into play. This string will hold down the second fret of G string. So basically, the two fingers which are currently on the frets are holding down the second frets of two different strings, B and G. You will be playing the F note on the G string.
The last finger i.e. your middle finger will be involved in holding down the second fret of the D string. So now you have all three fingers holding down the second fret of three different strings. This time you will be holding down E note of the D string.
Once you have managed to hold down the second fret of all these three strings, now you can play the chord. It depends upon you whether you want to leave the rest of the strings opened or you want to mute them.
Another way to hold the A chord is by using the first finger and making a bar on these D, G and B string so you can hold the second fret of these three strings together.