The numbers beside each row and above each column tell you the groups of filled squares, in order. "2 1" means 2 squares in a row, then a gap, then 1 square. Tap to fill. Long-press, right-click, or use × mode to mark squares you know are empty.
2 | 4 | 4 | 4 | 2 | |
|---|---|---|---|---|---|
| 1 1 | |||||
| 5 | |||||
| 5 | |||||
| 3 | |||||
| 1 |