The "X-Wing" is an advanced Судоку solving method that is based on two parallel rows or columns. You do not need to pay attention to the 3x3 blocks, as this strategy does not involve them.
This method will be easier to understand if you look at the example.
Давайте посмотрим на these two rows. They both have two cells that contain the candidate number 4. Since the number 4 cannot be repeated in the same row or column, we can safely assume that the 4s will be placed on a diagonal: either in the light blue cells or in the dark blue cells.
Now let's zoom out and look at the columns involved. Because the 4s are placed on a diagonal, both of these columns will now contain the number 4. Это означает we cannot place another 4 in these two columns.
Поэтому, we can confidently remove the candidate 4 from all the remaining заметки in these two columns.
Now that you know how to apply the "X-Wing" method in Судоку, you can continue to the next advanced strategy below, the "Y-Wing."