Each letter is worth a certain number of points. Common letters, like A and T, are worth only 1 point. Rare letters, like J and Z, are worth more.
In addition, there is a scoring bonus based on the length of the word. 2-letter words have no scoring bonus. But 3-letter words get a 2x bonus; 4-letter words get a 3x bonus; and so forth.
Finally, you'll get a bonus of 5 points for each unused draw pile card.