Question

what is helical motion

Answer 1

if a particle is given vertical velocity and magnetic field is uniform in x direction then it follows helical motion

Answer 2

the magnetic force is also perpendicular to the velocity resulting in circular motion. The speed and kinetic energy of the particle remain constant, but the direction is altered at each instant by the perpendicular magnetic force.
Thus, it has circular motion and moving forward as well, so it becomes helical in shape. Note that it's not spiral. It is spiral with forward motion in it. Like a spring