Why do things float? Why don’t other things do? Buoyancy answers these questions. The buoyant force is the net upwards force on a body in a fluid.$^5$
Like mentioned in the pressure section, when a body is submerged into a fluid, the pressure acts on it from all directions. However, the pressure at the bottom of the body will be greater, because the $h$ is greater. This means that, however slight, there is a difference in pressure on the bottom versus on the top of the body. If you assume that all of the pressure forces on the sides of the body cancel out, as they do, and only take the pressure forces at the top and bottom, you will see that there is a net force upwards. This force is called buoyancy.$^5$
When the weight of the body is less than the buoyancy force, then the body will float. When they are equal, they will cancel out and the body will remain still. When the weight of the body is greater, then the body will sink.$^5$
The buoyant force on an object equals to the weight of the fluid it displaces.
or
$F_B = w_{fl}$
Where $F_B$ is the buoyant force and $w_{fl}$ is the weight of the fluid.
This principle is true regardless of whether the object is fully or partially submerged.$^5$
In order to solve questions using this, in general, you must find the volume of the fluid displaced. If the object is fully submerged, then the easiest way to do this would be using the density formula($\rho = \frac{m}V$).