FOIL stands for First, Outside, Inside, and Last. It's a special case of the Distributive Property.
(x - 2) (x - 3) means that the first x gets distributed to the x (F) and the three (O). The 2 (I) gets it to the x and the three as well. (L)
(x - 2) (x - 3) = x² - 3x - 2x + 6 = x² - 5x + 6. (choice B)