How do intermolecular forces affect surface tension?
Intermolecular forces are forces that hold molecules together.
They attract each other (either in dipole-dipole or London forces) and hold each other together. This explains why solutions with higher intermolecular forces have a lower vapor pressure, higher boiling point, and is generally more viscous. The forces keep the outer layer of the liquid (surface) "together" until they are broken.
The water strider in the picture below can walk on water because the surface tension of the water can support its weight.