MasterMind is almost certainly a trademark of Invicta Plastics, and certainly not of me.
Behind the black squares at the top of the board is a random sequence of colours. Each square contains a particular colour (from the six options shown below the board), and each colour may appear any number of times.
Your task is to successfully deduce the correct colours in the correct sequence, by making suggestions on the board. You can do this by dragging a colour from the selection below the board onto the appropriate square in the current row -- starting with the bottom row (highlighted yellow). Once you have filled the highlighted row with colours, click "Score Row". You will then be told how many colours are correct, and how many are in the correct position. The grid to the right of the row tells you this:
Armed with this information, you should be able to successfully deduce the hidden colour sequence before you reach the top of the board.