Palming is a technique that allows you to hold or conceal an object in your hand. As the name suggests it involves hiding the object (for example, a coin) in the palm of your hand, although other versions of palming involve the use of your fingers or thumb.
When done skillfully, you should be able to palm a coin while conveying the impression that your hand is empty. Top magicians continue the illusion by maintaining unnatural hand positions with both hands so that the hand used to palm the object in question looks less noticeable.
There are three main palming techniques that can be used to conceal coins.
1) The Classic Palm: This is the most common method and involves holding a coin between the muscle at the base of the thumb and the fleshy part on the edge of the hand. The coin is kept in place using a small amount of lateral pressure. Ideally, you should use just enough pressure to keep the coin in place when your palm is facing down. Any more pressure will make your hand look unnatural and defeat the purpose of the palming technique. With practice you'll soon know the right amount of pressure to use.
When practising this technique there's a natural tendency to hold your thumb further away from your fingers in order to increase the amount of grip that you can apply to the hidden object. If possible, try to resist this temptation as it can give people a clue that your hand isn't as empty as you might like them to believe.
Try practising in front of a mirror until you can use the classic palm technique to hide coins of all shapes and weights in a natrual manner.
And when you start practising, it's a good idea to use the largest, yet lightest coin that you can find. For example, the American half dollar is a perfect size for practising and the fact that is has a strongly milled edge provides more grip. In contrast, smaller and heavier objects take more skill to palm naturally.
2) The Finger Palm: This is a slightly easier way to conceal a coin. From being displayed at the end of all five fingertips, the coin is released and slips down inside the hand to the crease in the skin where your fingers meet the palm of your hand. This allows you to hold the coin securely using a natural looking hand position. It also has the benefit that your hand can be viewed from a wide range of angles without revealing the coin.
Often magicians reinforce this technique by combining it with misdirection or picking up another object. This further reinforces the idea that their hand is empty.
3) The Back Palm: This method of palming is used to conceal a coin behind your hand, while showing your audience that the palm of your hand is empty. It's also the technique that magicians use when they pretend to pluck a coin out of the air or from behind a person's ear. In most cases the coin is gripped between the pinkey and the finger next to it. The other fingers and the thumb are then used to conceal the coin.