I'll assume that , and point along the x-, y- and z-axes, respectively. You see that along the path, , so the graph lies on the cylinder with radius 1 going along the x-axis. The x-coordinate grows linearly. If x(t) were constant, then y(t), z(t) would follow a circle. Therefore, this is a spiral. Further, (y(t), z(t)) make 2 revolutions when t ranges from 0 to , so when x(t) = 2t, there will be two revolutions when x ranges from 0 to .