The fingering for an A Major chord is a little more difficult than the C chord, especially if you have big fingers or a small guitar. The main thing is that you have to play the 2nd fret on the 2nd, 3rd, and 4th strings in order to play an A major chord. The fingering for an A major chord is shown below. Also, note that the chart shows exactly where your fingers should go for this fingering. The notes are staggered a bit along the second fret because there isn't enough room to align all three of your fretting fingers vertically across the neck:
Thus, the chart for the A major chord above tells us the following:
1st String - Play it open
2nd String - Put your ring finger on the 2nd fret
3rd String - Put your middle finger on the 2nd fret
4th String - Put your index finger on the 2nd fret
5th String - Play it open
6th String - Don't play it
So try it out. Put your fingers in place and strum it. It's OK if some notes don't ring. That's natural. Note that if another fingering feels better, then by all means go with that. I think Sean uses his ring finger to play the 3rd string, and his middle to play the 2nd string. He does this because it's easier to move to a D Major chord using this fingering (more on the D Major chord later in this lesson.)
Try playing the music example below, set your loop count to "Forever" in your preferences at the bottom of the page, hit the play button, wait for the music to start, and try to play along with the example. It'll help you become more comfortable with the chord.