Shade some of the squares in the grid, so that the numbers in each row and column match the lengths of its consecutive runs of shaded squares. A shaded square holds a purple square.
On a touch screen, a tap does what a click does, and a long press what a right-click does (more ways to right-click).
Click a square to turn it purple, then clear, then back to undecided. Right-click it to go the other way round, clear first.
With the keyboard, the arrow keys move a cursor around the board. Enter does what a click does to the square under it, and Space what a right-click does.
A square you know is not shaded can be marked clear: it turns yellow, with a faint cross. A gray square with nothing in it is one you have not decided yet.
Drag along a row or column to give every undecided square on it what the first square turned into. A drag whose first square turns back to undecided erases instead, and it erases a whole rectangle, not just a row or column. Hold Ctrl while moving the cursor to shade undecided squares as you go, Shift to mark them clear, and both to return any square to undecided. Like a drag, Ctrl or Shift alone leaves a square you have already marked as it is.
Hint explains the next step rather than simply making it. Each step works along one row or column at a time, from its numbers and the squares you have already marked purple or clear, so it carries on from wherever you are, as long as none of those is wrong; if one is, it asks you to fix the highlighted mistakes first. Its sentences call a square a cell.
A few ideas are worth learning by name:
On an Unreasonable board there comes a point where no row or column settles another cell on its own, and the hint says that nothing further follows by deduction instead of choosing for you. Save your position, try a cell, and it carries on from whatever you mark.
These parameters are available from the ‘Custom type…’ option on the ‘Type’ menu.