Run in a world full of letters and words, jump over letters or push them forward when you need a step. Mind the meanings of the words: when separate letters belong to a word, like 'er' to 'ladd' to form 'ladder', the shape of that word can suddenly change when the letters have been added. This can allow you to reach a higher ground, for example. Most words do (or let you do) what their names stand for: fall, ladder, stepladder and so on.
Use the arrow keys or A/D to move left and right. Press the up arrow or W to jump.