Toner is another word for a semi/demi/temporary hair color of your choice applied once hair has been bleached or pre-lightened light enough to achieve the desired shade.
After you highlight the hair, blow it dry and determine what color you are trying to neutralize with the toner. Apply the correct toner color and process according to directions.
Go to a professional and they will highlight your hair and after pulling the color up the hair dresser will put toner on your hair to keep it from appearing brassy.