solve

 sudoku

The Daily Telegraph rates this puzzle as a moderate level of dificulty.

The numbers given for this puzzle are in red.

Columns are c1 to c9
Rows r1 to r9
3x3 boxes 1 to 9

ie.the 3 in box1 is at c2r1

The rules -
Each column, row and 3x3 box must contain the numbers 1 to 9
It therefore follows that the cell where a row and a column cross must contain a number unique to that row and that column (and box).

See solution at step 23 to get the final picture of what we are trying to achieve.