Hold your hair between the tongs and basiclly wind your hair upwards towards your scalp and hold, i think.... My hair is naturally curly - even the frizz is natural too.
Basically wat u need to do is get a widish section of hair but not too thick and put the straighteners on a 45 degree angle to ur hair and slowly pull the straighteners down but at the same time rotating ur wrist. I think if u go onto the good hair day (ghd) website there is a short video explaining how to do it. hope this helps! i use them all the time to curl my hair which is poker straight and the curls last for ages!x
i find the best way to do it is by taking a section of your hair at the root, put the hair between the straightner irons like you would to straighten, but instead of pulling down ,lift the bottom of your hair and put over the top of the straightners then pull the straightners down..
its sort of hard to explain, but it always puts me in mind of when you would use a pair of scissors to make a ribbon curly....