I decided to buy some too so after getting the link from amazon ( thank you girls) and had a go on my self, something I hadn't done for over 10 years.
Stage one: apply the henna to oil,free clean skin, and let it dry of 2 hours
Stage two: once the henna has dried pick it off. The result is quite orange at this stage
Stage three : do not wash or bathe for another 15 hours at least and the colour of the henna will darken to a lovely brown.