How to complete a Sudoku Puzzle
Start by looking for which number occurs frequently in the puzzle.
Go section by section and ask yourself does this section need that number.
If the answer is yes, see if you can tell where it goes (remember you cannot have more than one of the same number in any row, column, or section).
If the answer is no, it does not need it, move to the next section. If there is only one place to put it that number, that is where it goes.
Keep going through the puzzle until most of it is filled in. Then look for rows, columns, or sections that are only missing one or two numbers.