A Naked Single is a cell that contains only one candidate, after filling in all the candidates for the puzzle.
Having only one candidate in a given cell, means that all other candidates have been elliminated, so the solution for the cell must be the remaining candidate.
If you already used the Single Search and the Snyder Notation strategies, it is unlikely you will find any Naked Singles.
If you tap on the following links on an iOS device which has the Sudoku Tutor app installed, it will launch the app and open the practice puzzle. Tap hint once the puzzle is open to see the strategy in action.Sample Puzzle 1 Sample Puzzle 2