This is a very easy game... but the instructions were unclear. According to some of the reviews below, people agree. Here's how to play: The words above (Dot, Special, etc) are units, later, powerups and little helpful things. Specials are stronger units depending on the book (castle) you have. Dots are weaker units. You can get new books in the upgrade screen (after the wave, there's 1 wave per level). However, you only have enough to summon a Dot. Type in the words that keep appearing for more mana. Remember to summon units to use up your mana!
As for a real review: Too easy (for the sake of completion, I grinded for the upgrades), instructions are too unclear. I can tell you tried making it harder because the words became longer as the game progressed and the enemy having new units (such as having a turret in level 12) but it's still too easy.