Energy flows in two directions. One towards the thumb, another towards the four fingertips.
Spreading palms as wide as you can, energy flows towards all five fingertips. Central holder is Jang-Shim located in center of palm, connected towards all five fingertips.
Thumb is slightly bent, slightly touching the side of your index finger. Four fingertips are sealed together and fingers are straight. Slightly focus on the end of your middle finger, with energy flowing towards the end of three fingertips (index, middle, and ring).
Bend the end of your fingers, like tiger palm. Central holder is Jang-Shim located in center of palm. However, energy does not shoot out but remains at the end of your fingertips
Thumb is slightly bent and about one finger-width apart from the side of your index finger. Slightly bend the end of the other four fingertips. You will feel energy flow/pressure moving towards the side of your palm, called Jang-gun.
How to make a fist
Open palms (as in Pig Foot above).
Roll your fingers so that all four fingertips touch the inside of your palm. This is important because when your impact with heavy resistance, it keeps your fingers from rolling back (avoiding injury to your palm bones, located behind the knuckles).
Roll further and feel the pressure of your four fingertips on the palm. As mentioned this keeps your fingers from rolling back.
Seal with your thumb on the first two (index and middle) fingers. Slightly squeeze upon impact. Before impact, keep not too tight or too loose.