Open the palm of your hand. Relax the hand. Take the index finger of your other hand and push on the fleshy area between the thumb and the base of the palm. Make sure your hand is relaxed. This is what raw meat feels like. (Check this out the next time you have a raw steak to cook.)
Now gently press the tip of your pinky and your thumb together. Again feel the fleshy area below the thumb. It should feel quite firm. This is what well done meat feels like when you press on it. (Check this out the next time you overcook a piece of meat.)
Press the tip of your ring finger and your thumb together. The flesh beneath the thumb should give a little more. This is what meat cooked to a medium doneness feels like.
Gently press the tip of your middle finger to the tip of your thumb. This is medium rare.
Press the tip of your index finger to the tip of your thumb. The fleshy area below the thumb should give quite a bit. This is what meat cooked to rare feels like. Open up your palm again and compare raw to rare.