The "Obvious Pairs" method has the same solving principle as the "Obvious Singles" method: you have to write the matching candidate numbers in all cells, and then look at the 3x3 blocks that have cells with two identical candidate numbers.
Let's look at an example to make it clearer. In the selected block, all cells are filled with candidate numbers and there are 3 cells with repeating digits:
- 2 and 8 (top left);
- 2 and 8 (top right);
- 1, 2 and 8 (bottom left);
The top two cells can only contain 2 or 8, the other numbers cannot (according to Sudoku rules). These will be our "Obvious Pairs", all that remains is to understand in which cell the 2 will be and in which cell the 8 will be. Then we look at the bottom left cell, there are candidate numbers 1, 2, and 8. But we've already figured out that 2 and 8 will be in the top cells, so we delete the numbers 2 and 8 from the bottom left cell, leaving the "Obvious Single" - 1. That's what we write in.
The "Obvious Pairs" method of solving Sudoku is interesting because it allows you to fill in the cells quickly with minimal risk of error.