Hey mate
The Law of Flotation says that for a floating object, the weight of the object equals the weight of the liquid displaced by the object. We prove this by using Archimedes' Principle with Newton's Second law applied to an object in equilibrium (floating).
The case that is relevant to the question is as follows:
[Note: The 'downward' direction is the direction of earth's gravity.]
When an object is immersed in a fluid, its weight (force caused by the gravity) will tend to pull it downwards. 

A fluid tends to exert pressure (due to the constant motion of its particles).

When an object is immersed, its base will be acted upon by the upward pressure of fluid. If the object is completely immersed, its upper half will also experience a pressure in the downward direction. The pressure pushing the object downwards will be lesser than the pressure upwards because of the difference in depth. (As the depth increases, the pressure increases.) 

Hope it helps