First, select the required board size and the number of mines. This is very important!
Then, fill the board with numbers for the squares you know. First, click on a number to select it. Then click the square on the board to set it.
Click on 'Find next move' or 'Find all moves' and the solver will check for possible moves
If a safe square is found it will be marked on the board with a green flag
If a mine is found it will be marked with a red flag
If the solver cannot find a definite solution, it will calculate for all the remaining squares the probability of being safe. It will then mark one square that has the highest chance of being safe with a green '?' symbol. For your next move, you will have to make a guess. You can either try the square marked with '?', or make your own guess.
Replace the green flags with the actual numbers and click 'Find next move' again