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.
Game Rule:
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)