There are a few different ways to cast on and this Long Tail Cast on is a nice stretchy one and is popular with knitters.
You use the tail of your yarn to create the stitches so make sure you have enough of a tail for all the stitches you want – to do this wrap your yarn around your needle for each stitch (so 30 wraps for 30 stitches) and then add a bit more to be safe.
Make a slip knot and place on your needle. Using your long tail and working yarn, with the long tail closest to you, pinch your thumb and index finger together and put them between the two strands. Wrap the rest of your fingers around the two strands and separate your thumb and index finger to create a diamond shape.
Insert your needle into the loop around your thumb going from the outside in, then (keeping that loop on your needle) insert the needle into the loop on your index finger, going from the outside in.
Finally carry the loop on your thumb up and over the needle. This leaves your new stitch and the original slip knot on your needle.
Pull your long tail to tighten the stitch.
