By default it uses the py-sudoku library. It generates a random sudoku based on the difficulty set in line 9 in Sudoku.py. Execution is done by hitting F5 while being in the Sudoky.py file. (At least in my VS Code).
You can setup your own sudoku to be solved by setting the board variable in the function GenerateSudoku.py to your own in the following template:
board = [
[7,8,0,4,0,0,1,2,0],
[6,0,0,0,7,5,0,0,9],
[0,0,0,6,0,1,0,7,8],
[0,0,7,0,4,0,2,6,0],
[0,0,1,0,5,0,9,3,0],
[9,0,4,0,6,0,0,0,5],
[0,7,0,3,0,0,0,1,2],
[1,2,0,0,0,7,4,0,0],
[0,4,9,2,0,6,0,0,7]
]