The objective of a picross puzzle is to fill in all the correct squares on the grid This is done by using the numbers on the side of each line, called hints, which represent how many continuous filled squares there are. For example, the below line has one number 5, which indicates that there are 5 consecutive filled cells.
When there is a space between the numbers, this indicates that a gap of at least one cell is needed between the two groups. A line with 2 2, means the line will consist of two consecutive fills, follwed by a gap of at least one, then another consecutive two fills.
TODO: sort control instructions
On mobile, tapping a cell multiple times will toggle its colour