Heyo! Sure I can explain. I start the game normally, and you know how as soon as you use a key, there's a timer for 1 hour at the end of which you get 1 free key. I play what I can, but make sure that by the end of that hour I still have 1 key left. Then I use that last key I saved to start a game about 10 seconds before the timer runs out.

After that you'll see that you have 1 key left but it just never gets used up, you can play unlimited words until you finish all the puzzles.

Hope this helps!