What does Newton's first law of motion tell us about velocity?

Every body continues in a state of rest or uniform motion in a straight line unless acted on by a resultant external force. That's approximately Newton's first law of motion.

So, the velocity of something tends to remain the same, unless an external force changes it. This is sometimes called "inertia". A body at rest, as in with "no velocity" will tend to remain at rest, unless there's a force on it. inertia again.