So I got the hair dye, lightening powder and 20 volume developer.

Do I mix all of this together all at once and put it on my head to dye my hair OR do I mix the developer with the lightening powder first to lighten my hair then wait like a day to put the color on it. If I lighten first, when I put the color on do I have to mix developer in with the color too? Not quite sure how to do this, thanks for your help!
I bought it and I didn't need a license, anyone can buy it