The goal of the game is to fill in the letters so that all rows and all columns are valid 4 letter words (according to Scrabble). The Hint button will populate the next empty square from a randomly chosen solution. When a row or column is completed a green check or red cross will appear indicating whether the word is valid or not.

Tap a square to select it, then tap a letter. On a keyboard you can also type directly and navigate with the arrow keys or TAB and <shift>TAB.