On the first day, you have either a black, blank square or a white one. This is the bottom right corner of the crossword. You may or may not have a clue, depending on whether it's a letter square or a black one.
On the second day, you have three squares, which may be black or white. If an low-numbered
clue is for a sufficiently long word, you may receive one or two clues at this point.
On the third day, you get five squares.
And so it continues until at the end of the week you're given thirteen squares. From this point the rest of the crossword can be predicted, but not the precise positions of each clue's starting point, so from then on you just get X,Y coordinates for each clue number plus the clues themselves.
You get extra points for predicting the crossword pattern and may be able to fill the words in beforehand. However, a guess cannot be taken back. Unless you record the sequence of squares in some way, they're lost until the end of the game.
This is delivered online, by email or even by post, and takes thirteen days to complete.