The unit of pressure
Because pressure is a force divided by an area, its unit is whatever you get when you divide the unit of force by the unit of area.
Force is measured in newtons (N) and area in square metres (m2), so the unit of pressure is newtons per square metre — that is, N m−2.
The pascal
In honour of the French scientist Blaise Pascal, this unit is also called the pascal (Pa).
1 N m−2 = 1 Pa
Pressure is a scalar
Force is a vector, carrying a direction as well as a size. Pressure has only a size, so pressure is a scalar quantity.
This holds so firmly that at a point inside a liquid the pressure takes the same value in every direction — something we shall see in section 15.2.
A common mistake
Saying "the pressure acts downwards" is not right. What acts downwards is the force. Pressure is just a number telling you how that force is spread over the area.
Remember
1 Pa is the pressure produced by a force of 1 N acting on an area of 1 m2.