Sudoku is a puzzle type popularized by nikoli.
All cells are regular. In an unsolved puzzle, each cell is either blank or has a number, but eventually all cells will be filled with a number between 1 and the length of the grid.
The basics in Sudoku is simple. Each row, column, and region must have all the numbers between 1 and the length of the grid, each number appearing exactly once.
Fill each cell with a number between 1 and the length of the grid such that each row, column, and region has each of the numbers exactly once.
Walkthrough of the example
Should I give it? First, note that R1C4 must be 1, since the only square in top-right box that is free for 1 is only that. A similar reasoning yields R3C2 to be 1. The new two clues make R4C3 to be 1. Repeat for each number.