You'll see a word and a grid of things. Tap anything you could point at and naturally call by that word, then submit your picks. Some options are close relatives, but not quite right, so choose carefully.
One set of four words unlocks per day, based on your device's clock. Everyone gets the same puzzle on a given calendar day, and it resets at midnight in your timezone. Select every tile that fits, then submit to lock in your picks for that word. Fourteen days are loaded right now. After Day 14 it loops back to Day 1 until more are added.
Easy: tap to select, tap again to change your mind before submitting.
Hard: once a tile is selected it's locked in, no take-backs. Choose carefully.