To do this achievement you are going to need some letters on the board. Basically the achievement title describes it all. Use 5 or more tiles from your rack to spell a 9 letter word. This is easier done playing a solo game because you can set the words up however you want them and don't have to worry about another player screwing your plays up. If you're not very good at spelling, or you don't want to think, check out magswordfinder.com.
Enter the letters you want to use in your word, and it will give you every word in the Scrabble dictionary with those letters in it.