Step 1: First Step
Well, first of all the one handed cut is a technique that many magicians use. It can come in handy in many magic tricks. So first off, hold the deck in your dominant hand as shown
Step 2: Step 2
Next, let go of about half of the deck with your Lower thumb. Doing that should make the deck look something like this.
Step 3: Step 3
Once you have successfully completed step 2, Take your index finger and push up the bottom half of the card deck making it look like so.
Step 4: Step 4
Next, bring your thumb back letting the deck go with it and push your index finger back.
Step 5: Final Step
After you push the bottom half to the left( if your a lefty) the rest should do its self!