Consider a magnetic field in positive x-direction. A charged particle enters this field at an angle of 30 degrees with the field. What will be the path traced by this particle?

Helical Path

Here velocity vector have two components 
(i) v cos $\theta$, parallel to magnetic field
(ii) v sin $\theta$, perpendicular to magnetic field. Due to component v cos $\theta$, the particle will have a linear motion but due to v sin $\theta$, the particle will have simultaneously a circular motion. The resultant of the two is a helical path.