THE RULES of Sudoku are simple:
Rule 1.
Each line must contain the numbers 1 to 9.
Rule 2.
No number can be repeated in the same line or column
Rule 3. No number can be repeated in the same
3x3 box.

Examples:

Rule 1:
Each line must contain the numbers 1 to 9

1 
2 
3 
10 
12 
3 
4 
8 
7 
2 
7 
4 
6 
9 
0 
8 
5 
3 
This is wrong,
because the numbers
10, 12 and 0 are used.

1 
3 
6 
5 
4 
3 
9 
8 
7 
2 
7 
4 
6 
9 
7 
1 
5 
3 
This is correct. 
Rule 2: No number can be repeated in the same line or column

1 
2 
3 
5 
5 
3 
4 
8 
7 
7 
6 
4 
1 
9 
3 
2 
5 
4 
This is wrong,
because the numbers 5
appear in the same row and number 3
appears twice in the same column.

1 
2 
3 
5 
5 
3 
4 
8 
7 
7 
6 
4 
1 
9 
3 
2 
5 
4 
This is correct. 
Rule 3: No number can be repeated in the same 3x3 box.

This is wrong,
because the number 2
appears twice times in the same 3x3 box.

This is correct. 
NOTE:
In Super Sudoku 3x4 grids, numbers
should be in the range 112
In Baby Sudoku 2x3 grids, numbers should be in the range 16
