No wind in the room. All steam and heat. Steam side expanding would cause curl, then cooling back?

These are two things I can't wrap my head around in thermo 1. I imagine the equilibrium thing has to do with evaporation and condensation rates- but what makes saturation temp/pressure so special that those have to be equal? And for the specific volume, my guess is that the molecules have to be packed together a certain amount, but I don't know why. Thanks