The difference between scalar and vector quantities is direction. A scalar has magnitude only. A vector has magnitude and a specific direction. This means a vector is not fully described until its direction is given, but a scalar is.
Look at matching pairs. Distance is the total length of a path, so it is a scalar. Displacement is the straight-line distance from the start to the finish in a stated direction, so it is a vector. A runner who completes one lap of a 400 m track has gone a distance of 400 m, but is back at the start, so the displacement is zero. A walker who goes 100 m east and then 100 m west has a distance of 200 m and a displacement of 0 m.
Speed and velocity are another pair. Two cars both travelling at 20 m/s, one north and one south, have the same speed but different velocities. Mass is a scalar, but weight is a force, so it is a vector.
