*If you don't know how to play this game, skip to "Game Rule" section.*
In this game, there is always a valid set on the screen. If you cannot find a set within 10 seconds, a "Hint" button will show up, which will either highlight a SET or draw new cards until there exists a SET on the screen.
The goal of this game is to find as many SETs as you can while minimizing the time and hints used.
Set (stylized as SET) is a real-time card game. The deck consists of 81 unique cards that vary in four features across three possibilities for each kind of feature: number of shapes (one, two, or three), shape (diamond, squiggle, oval), shading (solid, striped, or open), and color (red, green, or purple). Each possible combination of features (e.g. a card with [three] [striped] [green] [diamonds]) appears as a card precisely once in the deck.
In the game, certain combinations of three cards are said to make up a set. For each one of the four categories of features color, number, shape, and shading the three cards must display that feature as a) either all the same, or b) all different. Put another way: For each feature the three cards must avoid having two cards showing one version of the feature and the remaining card showing a different version.
For example, 3 solid red diamonds, 2 solid green squiggles, and 1 solid purple oval form a set, because the shadings of the three cards are all the same, while the numbers, the colors, and the shapes among the three cards are all different.
More details in https://en.wikipedia.org/wiki/Set_(card_game)