The single cast on knitting method is also called the thumb cast on, and backward
loop cast on. Whichever way you want to call it, it is one of the easiest ways of casting on in knitting.
It's so easy in fact that it's often used for teaching kids how to knit.
The backward loop cast on is very handy. It's great when you need to add a few stitches to your knitting. A knitting pattern may ask you to cast on a couple of stitches and this is the go-to cast on to use as it's fast and easy. This is when I use it the most.
It's also a great cast on method for lace projects because it creates a thin, loose edge.
For me personally though, it isn't my favorite cast on but I do know lots of knitters that love its simplicity. I find that the first row can be a little difficult to knit as the stitches tend to tighten up on the knitting needle. And if your tension is very loose you may end up with a row of loopy stitches. You just have to go slowly. Once you get through the first row everything is fine.
Try it and see what you think.
First of all start by making a slip knot. If you aren't sure how to make one you can review how to make a slip knot here.
Begin by holding your knitting needle with the slip knot in your right hand. Grasp the working yarn (ball end) in your left hand and grasp it with your fingers. Place your thumb over the yarn.
Bring your thumb down to loop the yarn around your thumb and bring your hand back up to an upright position.
With your knitting needle in your right hand insert it below the yarn at the base of your thumb using an upward motion.
Then just remove your thumb leaving the new loop on the knitting needle.
When the loop is on the knitting needle just gently pull it until it is snug on the needle - not too tight.
Continue until you cast on the amount of stitches you need.
Pretty simple right?
Below is a great video demonstrating this cast on method.