http://www.sudoku.com/howtoplay.html this shows you how to play it. i mainly play it to waste away time on the train and its a challange.

Looking at the example from KingLeonidas:(not mine):) __A B C D E F G H I 1. 7____5 8 3_____6 2. ____6_____1 4___5 3. __5 2_____6___8 3 4. 3_____2_____9 5 8 5. 5_______7 8___6__ 6. 6 4 8___1___3____ 7. __6___8___2 5____ 8. ____3 1 5_____7 2 9. 2 1 5 6_______3__ I'm passing the ones for now. 5B is a 2, b/c row 4 has a 2 and column C has a 2, in the big sq. 6H is a 2, b/c row 5 has a 2 & column I has a 2, in the big sq. You can continue that way w/ all the #s til 9. Another way is to either focus just on the rows or just on the columns.Looking at column A, the 1 in row 2 and the 1 in row 8 or the 1 being in big square (7-9; A-C), makes 3A a 1. Another way to consider eliminating is to pick a small sq. Let's say, 4B.Looking at 4B horizontally and vertically we can figure out the # by it not repeating. The 1 is taken at 9B, the 2 is in the big sq.(5B)and in row 4. The 3 is in 4A, the 4 is in 6B, the 5 is in 3B and 4H, the 6 is in the big sq.(6A) and 4B, the 7 is a possibility, the 8 is in the big sq. (6C) and 4I, the 9 is in 4G; so 4B is #7 b/c it doesn't repeat horiz., vert., and in the big square. I just covered 3 techniques. If those methods don't work you could write all the possible #s in each small sq. and by looking horiz., vert., & in the big sq.s make sure they don't repeat (making elimination a little easier). It's a popular game, because like crosswords, it keeps your mind stimulated while passing some time. There are different levels, and I like the easy-med ones. They say there is no guess work involved, but sometimes on the hard ones I have to guess twice. If you need anymore help, just ask :)

There are three 3 by 3 boxes, which makes 9 squares in each box, row, and line. You have to get numers 1-9 in every line, row and box, with no repeats. Its really only popular on long trips and when you have to pass the time.

It's a 3x3 grid (9 sections) with each section subdivided into 9 squares as well. You play by using logic to fill in the missing numbers based on the ones already provided. Each row, column, and 3x3 section can have the numbers 1-9 in it with no repeats. I enjoy it because I like challenging games of logic with simple rules. I usually only play Sudoku if I'm bored or on a flight or something like that, but it keeps my mind stimulated somewhat.