This simple trick is called the "throw away" card trick. For this trick, you have to place the card in your hand, snap it, and make the card in the hand appear to have disappeared. Here's how you do it:
# Hold your hand with the index and pinkie fingers up and the other three fingers touching each other, doing the old "Rock n' Roll" symbol.
# Place the card so the last inch or so (2.5 cm) tucks into the area between the middle and ring finger and thumb.
# Gently snap your fingers and straighten out your hand. The card will be clipped between the first and second finger and the third and fourth finger, and will appear to have disappeared. Just make sure you're facing the audience with your palm and they can't see the card on other side of your hand.
# If you get more skilled, you can practice bringing the card back and making it disappear again.