What is the role of intermolecular forces of attraction?
To keep molecules together.
All molecules are attracted to each other by dispersion forces. This force makes it so that molecules don't drive apart from each other, but stay together. Only when a large enough external force is applied can this force be broken (at least temporarily). Now this force is different for every molecule.
This makes water much more tightly-held together than other fluids. Those interactions are what you feel when you jump in a pool, but hit the water surface with your body horizontal. It hurts, because the water wants to stay together instead of letting you through.