First, start off by holding the guitar in the most comfortable way possible. Your palm should be holding the guitar from the bottom while your thumb should be gripping the neck.
Once you have done holding the guitar, prepare your index finger, middle finger and ring finger to play this chord.
The A minor chord is somewhat like an A major chord, but the only difference is of what you play on the B string.
Leave the last string open. This means that the E string will be left ringing. However, it depends whether you want to mute it or not.
Use your index finger to hold down the first fret of the second last string. This basically means that you will be holding down the C note of the B string.
Your ring finger will hold down the second fret of the third last string. This means that you will be playing the A note of the G string with your third finger.
The last fret you need to hold down is on the fourth last string. Use your middle finger to play the second note of this string. In musical terms you will be playing the E note of the D string.
The A string will be left open because you are playing an A minor chord and the A note must be left ringing.
The first string should be muted in case you want an A minor chord to sound just perfect.
Your chord progression in notations will look something like this: X 0 2 2 1 0.
Some people even play it like: X 0 2 2 1 X.