The numbers beside each row and above each column tell you the lengths of the filled runs in that line, in order, with at least one gap between runs. Deduce which cells are filled.
Fill mode — click or tap to fill a cell. Drag across a line to paint a whole run at once.
Mark mode — place an X to note a cell you know is empty. On desktop, right-click always marks. On touch, long-press marks.
Win when the filled cells match the hidden picture. X marks don't count — only the fills.