This is one of the simple ways to cut cards using only one hand. There are other more complex ways of cutting, but I only know of three ways of doing it and the other two ways that I know of, I kind of trailed off to other tricks before mastering them.
The only materials you need is a deck of cards and one of your hands (keep the other close by in case the cards start to fly).
Step 1: Position the cards and drop half
Position the cards as shown in the photo. Use your pinky finger as a guide to prevent stray cards from dropping.
Now tilt your thumb forward until approx. half the deck falls into the cradle created by your hand.