The incantation is represented by the characters in the upper left corner of each image. The chanted words say 临兵斗者，皆数组前行 (Lín bīng dòu zhě, jiē shùzǔ qián xíng), which means, literally, "provisional soldiers of the Northern Bushel are all arrayed in a line." "Provisional soldiers" is probably a term for certain kinds of military troops. The Northern Bushel is a constellation, also known as the Seven Stars, which corresponds to the Big Dipper; it's supposed to be the best source of celestial power in Daoist ritual. So the chant is saying, basically, "The bad-ass fighting spirits of the stars are on my side." It's performative speech, as rituals go; it says things are this way while it makes them be this way. The hand seals correspond in ways I don't quite grok--there's a lot of Yì Jīng-based numerology--but they serve to strengthen and amplify the intoned words. Dàoshi will call upon the armies of spirits to drive away misfortune, to exorcise ghosts, to scare tigers away, to help people win at gambling, and so on.