Hints help you reveal the letter of a selected cell, making it easier to solve the grids. At the start of the game, you receive 6 hints as a welcome pack.
If you run out of hints, you can collect more by watching an ad through the Hint button located at the bottom left of your keyboard.
You can also get additional hints by watching an ad after completing a level (with 3 stars), with the Daily Bonus, or by earning a new badge.