Sudoku Solver in Python - Can someone explain this code ?

[qwemx]

def Suduko(grid, row, col):
 
    if (row == M - 1 and col == M):
        return True
    if col == M:
        row += 1
        col = 0
    if grid[row][col] > 0:
        return Suduko(grid, row, col + 1)
    for num in range(1, M + 1, 1): 
     
        if solve(grid, row, col, num):
         
            grid[row][col] = num            
            if Suduko(grid, row, col + 1):
                return True
        grid[row][col] = 0
    return False

I am not sure if we are using row=0 and col=0 as starting or row=1,col=1 as starting
In this code the Row = 8 and Col=9 because M=9
so if we see the picture attached.

suduko rows and column

so we still have one more Row left at the bottom - how will that be processes?


so basically we have two functions suduko and solve
I am trying to study what exactly each doing.