In a liquid the molecules which are closest to the surface has a net force downwards. But how it helps them to store potential energy? And to minimize the potential energy the surface area shrinks forming a circular shape. How forming a circular shape helps to reduce stored potential energy?
In brief, minimizing the surface area of condensed matter releases (not stores) the maximum amount of energy.
Surface molecules generally feature unsatisfied bonds because it's not possible for bonds to form in all directions, as they would in the bulk. This situation is equivalent to an energy penalty for every unit of surface area that exists. This penalty can drive surface reconstruction, for example, in which the state of bonding near the surface changes form, density, orientation, and so on. It also drives spontaneous reduction of the surface area. (A reduction in energy over a distance is equivalent to a force, which we call surface tension.)
Thus, a drop of water in 0 g spontaneously forms a sphere. In this way, the maximum number of molecules are on the inside, forming fully satisfied bonds with the neighboring molecules and thus releasing the maximum possible amount of energy to the surrounding environment.
Forming bonds releases energy. I can see you are aware of that from the comments.
Now, how can a liquid form as many bonds as possible and reduce the number of unsatisfied, unformed possible bonds as much as possible? It can do that by giving all molecules as many neighbours as possible to bond with.
And which molecules have the least neighbours? Those at the surface.
So this essentially comes down to reducing the surface area as much as possible.
- And which shape has the smallest surface area? That happens to be a ball.
You can see that simply by calculating the surface area of a ball and comparing it with surfaces areas of other shapes with the same volume.