Classical mechanics
When something moves, its position changes. You may pull a book closer to you, and the book has a new position. Or, you may walk away from your house and you have a new position. The velocity of an object tells you how fast the object changes position, and where it is moving. Velocity is a vector just like position: a car can move "160 kilometers per hour west" (100 miles per hour west) or "31 miles per hour south" (50 kilometers per hour south). Since position can be negative, velocity can be negative too.