Entering a Puzzle
If necessary, clear the puzzle grid by tapping New. Tap any number of squares. Then tap the associated numbers in the same order. Correct mistakes with the red ⊲-key.
or
Select a number, then tap all cells that should receive the number in the puzzle grid.
or
Paste a text-formatted puzzle into the text field. Tap 'Done' on the keyboard or long-press the background.

Text format: 81 characters ordered top-left to bottom-right of the puzzle grid. Empty squares are represented by a decimal point or the number zero.
Example:
938.24....1........56..7.. etc.

Delete squares with the red ✗-key.

Loading a Puzzle
To load a random library puzzle, tap on the library symbol in the top-right corner.
or
To select a specific puzzle, tap on the puzzle title (iPhone: center of navigation bar).

The difficulty level of the puzzle is shown below the title: Easy - Medium - Hard - Unfair - Extreme.

The high score of a previously solved puzzle is shown along with the title. Tap Reset Score to clear the score for either the current puzzle or for all puzzles.

Checking a Puzzle
(Optional) Tap on Check. Smart Sudoku tries to determine whether a unique solution exists. The test will be aborted if it takes more than about 8 seconds. The time-out doesn't necessarily mean that the puzzle doesn't have a unique solution.
The message No unique solution in most cases is caused by a wrong or missing number in the puzzle.

Solving a Puzzle
Slide the switch at the bottom to Start solving. If the puzzle has a unique solution, the green input numbers will appear as gray clues. To enter a solution number:

Tap the number, then tap the requested square.

or (recommended):

Tap as many squares sharing the same solution number, then tap the number. Solving two or more squares in this way improves your score, reflected by the growing progress bar below the text field.
The current score is also shown numerically in the top bar.

Solve
To ask Smart Sudoku to solve a puzzle fully or partly for you, tap on Solve. By displaying the full solution, you will permanently lose all score points.
Solve an arbitrary single square by selecting it, then tapping Solve.
Solve any number completely by selecting it, then tapping Solve.
In the latter two cases scoring will restart at zero.

Hint
Tap Hint and Smart Sudoku will tell you what standard Sudoku pattern to look for next, i.e. a Naked Triple. Dismiss the dialogue if you want to find the pattern yourself. Otherwise tap the dialogue to see the squares involved.
The Sudoku pattern is colored yellow, the squares which may contain candidates to be eliminated are colored blue. If candidates are on, the pattern's numbers are shown in red on the keyboard. Simply tap them to eliminate these candidates.

Smart Sudoku detects Naked and Hidden Singles, Pairs, Triples, Quads, Quintuples, as well as Locked Candidates Type 1 and 2, X-Wings, XY-Wings, XYZ-Wings, W-Wings, Skyscraper, 2-String Kite, Swordfish, Jellyfish, Empty Rectangle and Unique Rectangle Type 1 and 2.

On extremely hard Sudokus, it may run out of hints and you will have to apply even more sophisticated strategies. One nice way to do this is to copy the puzzle from Smart Sudoku (tap on the text field at the top) and paste it into an online Sudoku Solver like www.sudokuwiki.org/sudoku.htm (click Sudoku Solver, then Import a Sudoku).

Candidates
Tap Candidates (or double-tap the background) at any time and as often as you wish in order to show or hide legal numbers (candidates) for all squares. To eliminate a candidate:

Tap a number, then tap the squares where this number should be eliminated as a candidate.
or
Select an arbitrary number of squares, then tap the numbers to be eliminated from these squares.

With no square selected, tap a keyboard number to see all squares having that number as candidate.

Smart Sudoku will not let you remove the solution of a square by eliminating candidates. Attempting to eliminate the last candidate of a square will automatically convert it to the square's solution.

Miscellaneous

Undo/Redo
You may undo or redo any step of your solution path.

Copy/Paste
Copy a puzzle to the pasteboard anytime in order to paste it into any program capable of receiving text. In the entry mode of Smart Sudoku paste a puzzle from the pasteboard into the text field. Thousands of puzzles formatted as text are available on the Internet as well as on the homepage of Smart Sudoku.

Sharing a Puzzle
Share your favorite puzzles with friends. Challenge them to beat your score. Or send them the state of a puzzle at which you had to give up. Simply tap on the share symbol in the top-left corner.

Deselect
Deselect all selected squares and keyboard number keys by tapping Deselect. Alternatively, triple-tap the puzzle or the background.

Changing the background image
Swipe right the background or puzzle to select the next of pattern, swipe left to select the previous pattern.