Click a square - it should turn green. If you type a 0 (the number zero) it will turn the square black. There may be up to three other squares that also turn black since it's symmetrical. If you type a 1 (the number one) it will turn the square white. Handy for erasing mistakes.

Inserting letters - First, set the direction by clicking the button in the top left. It toggles between Across and Down. Click a square - it should turn green. Type a letter - the green moves to the next square. Type another letter etc and press the spacebar when you've finished.

Clear button - clicking this completely clears the grid. Allows you to start from scratch.

As long as you have cookies enabled, the page should remember your entries so that you can leave the page and come back to it.

Numbers button - this toggles clue numbers on and off. They will only be correct when you've got the grid correct.

Search button - if you have some letters in a word, set the direction and click an empty square in the word. Optionally enter a keyword in the box next to the Search button. Click the Search button. If you select a word and click Ok, it will be inserted into the grid.