Find the maximum number of words using the proposed letter.
With enough found words, you access the "Panic event" that offer a new list of letters but less time...
You can collect "Ad coin" when you activate a panic event.
Then, you use your "Ad coin" to unlock game mode.
On Android, watching advertisement with this button before a game provide also some "Ad coin" as reward.
Warning: as requested in Europe (GDPR), each player has to agree (on options screen) to look at advertisements.