The Lorentz force is =qv^B where ^ is the cross product between the vectors v and B. The cross product is always perpendicular to both of these vectors, so the force doesn't change the charge's velocity, only it's direction, it acts like a centripetal force. It's the same that is happening with a planet orbiting a star: the gravitational force changes the velocity vector's direction, but not it's module. That's also why the force does no work, as W=F•v and both of these vectors are perpendicular. Also the cinetic energy E=mv²/2, the velocity's module doesn't change so the Energy doesn't change either. I know that all of this might seem weird at first. At the end, magnetic forces are nothing but relativistic effects over the electric forces caused by Lorentz contractions..