An object floats in a liquid if its density is less than that of the liquid. If its density is greater than that of the liquid it sinks!

When an object floats in a liquid the upthrust is equal to the weight of the object itself - the net force on the object is zero.
A floating object displaces its own weight of liquid.

The density of the liquid is important - objects float 'higher' in liquids with a high density.