A vector is defined as an object that has both magnitude and direction. Geometrically if you have to picture a vector as a directed line segment, the length will represent the magnitude of the vector and the arrow will indicate the direction of the vector (direction of the vector is from head to tail).
A simple example is that John is travelling at 120km/hour heading south. This is an example of a vector because we given both magnitude and direction. The opposite of a vector would be a scalar. A scalar quantity contains magnitude, looking at the example previously given, scalar would only be the speed of 120 km/hr that John was travelling at (contains no direction, DO NOT CONFUSE!)
Example of quantities that are vectors: