This page contains sudokus, but they are slightly different from regular sudokus. This is how sudokus work:

Every

These are the kind of clues you can get:

If a square looks like this, you know it contains the number written in it. | |

If a square looks like this you are not given any clue regarding what is in it. It could be any number from one to nine. | |

If a square looks like this you know it does not contain any of the numbers which are covered. In this case the square does not contain eight or nine. |