The concept is simple. Each number represents a letter, so, starting with the solved letters, use your logic and vocabulary to reveal more letters, form words, and then crack the code! The Codeword series is so popular because you don't need any prior knowledge, unlike a crossword. You can just pick up a pen and get puzzling. It steadily increases your vocabulary, as the difficulty slowly grows as you progress through the book, and even though you'll be working your brain, it's the perfect way to unwind.