Sontaj is a puzzle game that is very much like Sudoku. It uses letters inside circles instead of numbers. Sometimes the game will use both letters and numbers.
To win the game, you must fill in the grid using logic. You have to find the missing letters without repeating any.

Look for a row, column, or square that is almost full. Count the letters that are already there.
Check your letters from A to I. Find which ones are not on the list.
Look at the empty circles in that row or column. Check the nearby squares and columns.
Every time you fill in a circle, look closely at the grid.
Keep using this logic for other rows, columns, and squares. The game is won when every single circle is filled and no letters are repeated.