Pick your size crystal you want to work with and use the corresponding nib for the applicator, screw this on - make sure to do this when the tool isn't turned on as it gets very hot. Turn your applicator on and wait for it to heat up. 

Now pick up your chosen size crystal with the tool and place where you want it to go on your chosen item of clothing or accessory, it should stick in place and after it has cooled it will be glued in place. Repeat until you have your desired look. 

Important Notice - This tool gets extremely hot, do take care when using so you do not burn yourself.