Fire up UMK3 either against CPU, another controller or online. Select Human Subzero, defeat the other character and once the game says finish him\her position yourself so you are touching the other(face to face) and then quickly press...
Block, Block, Run, Block, Run
... if done correctly fatality should commence. That is the easiest one to do but you can of course use any character in any game
Remember that you can see a complete move list on the pause screen via select and also you can bind actions to any buttons you want to make remembering the combos easier.