This is how I learned on how to make slipknot.
To make the slipknot on your hook, follow the step-by-step photo tutorial below.
Hold the yarn and hook properly, or whichever you are comfortable with. Grab the yarn using your hook.
While holding the grabbed yarn on the hook, turn the hook counterclockwise as shown on photos above.
This is how it looks like after turning your hook.
Grab the yarn again and pull the yarn through the loop. Pull the tail of the yarn firmly to tighten the knot.
Make sure your completed slipknot is tighten enough that you can barely slide the hook on its loop for next stitch to be made.
Girlie's Crochet > How to Make Slipknot