100:9 The kohanim raise their hands to the level of their shoulders and spread them out. They separate their fingers so that there are five spaces altogether as follows: between two fingers and two fingers, there is one space; between two fingers and the thumb there is one space; the same is done on the other hand, making four spaces; between the two thumbs there is an open space, making a total of five. They do this because of Shir HaShirim 2:9, “He (meaning G-d) peers through the lattice.” The right hand must be raised slightly over the left so that the right thumb is over the left thumb. The kohanim spread their hands so that the palms face the ground and the back of their hands face Heaven.
100:10 When the kohanim bless the people, they shouldn’t look around or let their thoughts wander. Rather, they should look downward as one does when praying. The congregation should pay attention to the blessing. They should face the kohanim but they shouldn’t look at them (neither their faces nor their hands, so that one should not be distracted from the blessings – Mishnah Brurah 128:89). Also, the kohanim should not look at their hands; the practice is to let the folds of the tallis cover their faces. Their hands are outside the tallis (such is not our practice – see Rema 128:23 and MB 128:91). The congregation also fold their talleisim over their faces so that they shouldn’t look.