The most fundamental Christian gesture — a physical confession of the Trinity and the cross.
Orthodox Christians make the Sign of the Cross with the right hand, joining the thumb, index finger, and middle finger together (representing the three Persons of the Trinity), with the ring finger and pinky pressed against the palm (representing the two natures of Christ — divine and human).
The gesture goes from the forehead to the chest, then from the right shoulder to the left shoulder — the opposite order of the Western form. The Western change to left-then-right developed in the early medieval period.