To unlock this achievement you need to play 100 FULL 2 minute games of wordament.
You can not jump into a game and jump out and keep doing this. It will not count.
You can view how many game you have completed by going to "Leaderboards" then click the "Me" button at the top.
Note: If you have played wordament on a windows phone and unlocked this achievement:
then this will unlock in your first game on windows 8 as they it will use your scores from your windows phone.