The rules are simple.

The goal is to reduce all the numbers on the board by reducing pairs of numbers.

Two cells are reduced if the numbers in them are the same or their sum is 10. If this condition is met, a dot is placed in both cells instead of the numbers, and these cells are no longer part of the game.

The cells selected for reduction must be adjacent horizontally or vertically (not diagonally!). Cells that are only separated by empty (blanked-out) cells are also considered adjacent. Moreover, since the cells are viewed from left to right and top to bottom, the adjacent cells are also considered, for example, the cells with coordinates (1,1) and (8,5), if all the cells between them are empty "along the viewing path."
If there is nothing to reduce, but there are still cells with numbers on the field, the button for adding new numbers is pressed. In this case, the remaining numbers are added to the tail of the table in order, from left to right and top to bottom. Now they are also involved in the game.

This way, the player can pass the time and enjoy the game.

Control in the game:
selection of numbers is carried out by the mouse, it is also on the right mouse button or spacebar called a hint, the mouse wheel can scroll the list of numbers when it becomes large

Also I draw your attention to the fact that you should not especially trust "Hint": it is a little stupid, it does not know how to analyze yet, it just looks at all the cells in order and shows the first reduced combination, which is not always optimal in some cases. In fact, it is useful only when there are many cells on the playing field and it is difficult for you to cover everything with your keen eye.

There are 2 difficulties in the game (classic and difficult), and you can't choose them yourself. At first, the classic difficulty is available, where you always have the same number layout. However, once you've completed the game and reduced all the numbers, you can restart the game, and you'll have a random number layout that will make the game much more challenging. The average completion time for the classic difficulty is between 6 and 30 minutes, as I have personally tested.