Speed of an object is the ratio of the distance traveled to time taken and is mathematically given as:
Speed = Distance/time
Velocity of an object, on the other hand, is the ratio of displacement of the object to the time taken and is mathematically given as:
Velocity = displacement/time
Speed is a scalar quantity, that is, it has only a magnitude and no direction. Velocity, in comparison, is a vector quantity and has both the magnitude and direction. If there is some motion, speed cannot be zero, since distance traveled would be a non-zero quantity (if motion took place). In comparison, velocity of an object can be zero, even if the motion tool place. This is because displacement of an object can be zero (consider object moving in a circle or someone moving towards east and then the same distance along west, etc.).
Hope this helps.