A physical quantity is something that can be measured. Scalar quantities only have a magnitude.
Some examples of scalar quantities that refer to motion include:
Scalar quantities can be added by just adding their values together.
A car increases its speed by 12 m/s when it is already travelling at 6 m/s. Calculate its new speed.
12 + 6 = 18 m/s
Scalar quantities can be subtracted by subtracting one value from another.
A man walks a distance of 350 m. His home is 1000 m away. Calculate how far he needs to walk to get home.
1000 - 350 = 650 m