Knit on cast on

From BluWiki

This is done similar to the knit stitch. First you tie a slip knot onto your needle. Then you insert the needle as if to knit

wrap the yarn as if to knit

pull the loop through as if knitting

Only this time, instead of taking the old stitch off the right hand needle, you put the new stitch onto the right hand needle.

The video demonstrating this is here.