Archimedes Principle states - When a body is immersed completely or partially in a fluid it experiences an upward force that is equal to the weight of the fluid displaced by it
Take a piece of stone and tie it one end of a rubber string. Measure the length of rubber string. Now suspend the stone by holding the string and again measure the length of rubber string during suspension
You will find that elongation of the string due to weight decreases as the stone is gradually dipped in water. But there is no further change once the stone gets fully immersed in water because The elongation is produced in the string due to the weight of stone. The extension decreases when stone is lowered in the water ; it means that some force acts on the stone in upward direction. As a result, the buoyant force & its nature in different fluids for a given body can determined by archimedes principle.