The numbers are the lengths of the runs of filled cells in that row or column, in order. Runs are separated by at least one empty cell.
Click fills a cell · right-click (or the ✕ Mark tool) notes an empty one · drag to paint a line · ↩ Undo takes back a stroke.
Clues fade when their line is complete. Every puzzle has exactly one solution and needs zero guessing — start with the big numbers.