Each picture is hidden in the grid. The numbers beside every row and above every column tell you where to fill in squares.
A number is a run of filled squares in a row. 3 means three filled squares side by side. 2 1 means a run of 2, then at least one empty square, then a run of 1.
Tap or drag to fill squares. Use Mark X (or right-click) to mark squares you know are empty. Marks are only notes, they do not count.
A number turns grey when its line is right. Start with big numbers and with lines that are full or empty. Every picture can be solved by logic, so you never need to guess.
Stuck? Hint fixes one square for you, and Undo takes back your last move.