Open your left hand flat. Now press on the fleshy bit by your left thumb with your right index finger. That's how a raw steak should feel.
Now, using your LEFT index finger, curl to into your palm and press the same fleshy bit near your thumb. That's how a rare steak should feel.
Repeat with your middle, ring and little fingers for medium rare, medium and welldone.
As you progress through the finger, you have to tighten the muscle near the thumb to reach the further fingers which makes it more firm and hence makes it feel like the meat cooking.