Scraping the tongue removes bacteria and toxic metabolic substances of the gut which are produced in the process of digestion and deposited on the tongue.  You can see it during scraping.  The white, yellowish, gray or different color coating means there are millions of bacteria living there.  It should be cleaned away for good digestion, as digestion begins in the mouth.  

The build up of bacteria on the tongue causes bad breath, and according to Ayurveda various types of digestive and respiratory problems.

A tongue cleaner should be made of a pure and unalloyed element such as copper, which imparts considerable benefits to the human body.  We never recommend cleaners made of processed materials like plastics.  

Use before you eat breakfast.

Brush and floss your teeth and never, never brush your tongue.

Take the two ends of the scraper in your hand, and reach the arch to the back of the tongue.  Scrape forward several times, rinsing the white mucous off the scraper between scrapings.  Rinse the mouth once you are done.