If you get stuck on a Sudoku board and can't see a clear solution for the remaining cells, you can use "notes." With the help of notes, you can fill in all possible options for each empty cell, paying close attention to the numbers already on the board.
It is very important to fill in the notes correctly. If you make a mistake, solving the Sudoku will become much more difficult and time-consuming.
After placing your notes, you will find it easier to understand where the numbers should go. Furthermore, many advanced Sudoku-solving techniques are based on the use of notes. You can learn about such techniques in the lessons on our website, lovesudoku.net.