Some things we talk about in Physics are fully described by a number and a unit. A few examples might be
2.6 kg of apples from the grocery store
18.5 yd2 of carpeting for your apartment
15.8 m2 of carpeting for your apartment
15.2 gallons of gasoline at the filling station
28.3 liters of gasoline at the filling station
35 lb/in2 air pressure in your tires
135 kPa air pressure in your tires
98.6o F is normal body temperature
39o C is normal body temperature
Things like these are called scalars. Scalars are fully specified or completely described by a number and a unit. (Don't forget the unit! Units are important!).
Some other things we talk about in Physics also need a direction. Some examples include
Montreal is 600 km east of Toronto.
Chicago is 300 km north of Charleston.
The wind is blowing 30 km/hr from the north (brrrrr!)
The force of gravity is 500 N, down.
The table's support force if 350 N, upward.
The force of friction is 110 N, to the left.
The string exerts a force of 55 N, at 40o above the horizontal.
Things like these are called vectors. Vectors need a direction to fully describe them. Vectors require a number, a unit, and a direction. (Don't forget the units! Units are important!).