"Across" indicates words to be entered horizontally, "Down" indicates vertical words. You can either click on a number in the puzzle to highlight the corresponding question, or click on the question directly in the list. The corresponding word will then be highlighted in gray. Now type your proposed solution using your keyboard and press "Enter". If you have typed correctly, your entry will turn green. If you were wrong, it will turn red. You can undo entries you have already made by clicking the "Delete" key on your keyboard or your phone.