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Flotation means thrust and  pressure. 
1.Trust:- The force acting normally (perpendicular) on a surface is called thrust. The thrust is a vector quantity and is measured in the units of force i.e., Newton (N) and kilogram force.
2. Pressure:- Pressure is defined as the thrust acting per unit area of a body mathematically we have Pressure= Thrust  Area   Pressure is measured in SI in Newton per square metre (Nm-2) or Pascal. And it is also measured in bar and millibars. (1bar=10sN\m2 and 1 millibar = 10m\s2).
Fluid: Fluid is a substance that flows.  For example, liquids and gases. They take the shape of container in which they are stored.
THRUST:  The normal force acting on a unit surface area of the fluid is called thrust
Density: The mass per unit volume of a substance is called density.