Your task is to place 81 tiles onto a 24x24 game board. Each tile is a 2x2 grid of coloured squares, with each quadrant being one of three colours. (in CGA days, when it came out, this would be bright teal, magenta, and white, but let's just use red, green, and blue for this discussion). A tile might look like this:
You try to place like colours next to like colours. The score of any block of adjacent colours (horizonal and vertical, not diagonal) is the square of the number of squares of that colour. So you really want to make the largest contiguous area of one colour that you can, perhaps choosing one colour over another.
To further demonstrate scoring, consider this game board:
Average scores in the game were 12,000-14,000. High scores were around 17,000.
In theory this is a solvable (maximum high score) game. 81 tiles, known scoring, it could be brute-forced. But that's a lot of tiles. As far as I know it has not been solved.
And I apologize for not making it sound like a fun game. It really is. Simple, abstract, and fast, with onlookers and others willing to try, it can become quite the competition.