Slide one tile at a time. Letters lock into a real English word when they line up. Then smash two of those words together into a compound. CAT into FISH. CATFISH. Play is untimed. Bigger boards show more words at once. Timed smash-up is a separate 7x7 / 8x8 race: smash every compound before the clock runs out. A small word adds a few seconds; a smash adds more.