1.
Hold onto your yarn at two points, ensuring you're at least a few inches away from the end of the yarn. The tail (and end of your yarn) should be to the left and your ball of yarn should be to the right.
Tip: The tail is the yarn which goes from your work to the end of the yarn, whereas the working yarn is the yarn which goes from your work to the ball of yarn.
2.
Place the yarn in your right hand on top of the yarn in your left hand to create a loop. Hold onto the loop with your left hand.
3.
Bring your right hand to the back of the loop and insert your thumb and index finger through the loop.
4.
Grab the tail of yarn and pull it slightly back through the loop and pull on the strands of yarn as you do this, so you've created a new loop and closed the original loop. This loop is your slip knot.