The "Last remaining cell" is another basic Sudoku strategy. It is based on the fact that a number cannot be repeated in each 3x3 block, each row, or each column.
Let's look at an example with a 3x3 block. The number 8 must be placed in this block. However, an intersecting row and an intersecting column already contain an 8. Since we know numbers cannot be repeated, we cannot place our 8 in the cells where that row and column cross into the block. This means there is only one cell remaining inside the block where the 8 must go.
The same solving method also applies to rows and columns.
This is how you use the "Last remaining cell" technique when solving Sudoku. Once you have learned it, you can move on to the next Sudoku strategy.