A dear friend gifted me with this prayer cord, from Ukraine. Made by monks, one can see how Byzantine it looks.
With each breath (air inhaled and exhaled), with each knot/bead, one prays, "Lord Jesus Christ, Son of God, have mercy upon me, a sinner." This is a fantastic devotion and easy for anybody.
Read about the Jesus Prayer in the Catechism of the Catholic Church, number 2616.