KenKen puzzles are grids of various sizes in which you have to place certain numbers in certain positions. The rules guiding which numbers you can place where are relatively simple and are similar to those in sudoku [sources: KenKen, McCarthy,].
The numbers from which you can choose are dictated by grid size. With a 3-by-3 puzzle, use numbers one through three; a 4-by-4 puzzle uses one through four and so on, up to 9-by-9 puzzles. Numbers cannot be repeated in any row or column [source: KenKen].
Within each grid, there are darker lines denoting variously-sized cages. A cage can be just one square, or cube, or several cubes that cross rows and columns, forming Ls, Ts and other shapes. Each cage contains a number and math operation. The numbers you place in each cage must combine to form the number using the math operation specified. So let's say there's a two-cube cage with "3+" in it. That means the numbers you put in the two cubes have to total three when added. Your choices, then, are one and two (1+2=3). Easy, except you also have to figure out which number goes in which square -- and that's impacted by the cubes and cages around it [source: McCarthy].
If a cage contains only one box, enter in the puzzle number indicated in the top corner. You can use a number more than once within a cage, provided it's not repeated in the same row or column [source: KenKen].