Summary

Change in electric potential energy for charge moving between 2 potentials \Delta U_E=q\Delta V (J)
q can be positive or negative. \Delta V=V_{final}-V_{initial}.
Energy is conserved: \Delta K=-\Delta U_E
Positive charges speed up moving towards lower potential. Negative charges speed up moving towards higher potential.
Electric field points towards decreasing potential.
For particle starting at rest, kinetic energy gained equals magnitude of q\Delta V, lets you solve for final speed.