Shake the bottle really well, then spray onto a dry wheel in a sweeping motion. Do one wheel at a time, making sure to get good coverage. If the product does not get on all the brake dust and grime in the wheel, it cannot clean it off. This is why we like to suggest using a wheel brush like our Little Chubby brush. It has a 'unique' smell - that's normal. If you're the rare one who is a bit sensitive to it, we would suggest wearing a mask.
Leave it on the wheel for about 30 seconds to 1 minute, until you start to see the liquid turn purple.