While the most basic necessary components of a paint are a binder and a pigment, they also contain a solvent. The role of the solvent is to dissolve it all into a liquid and allow for better application.
A paint is usually either water- or solvent-based (sometimes called oil-based), and it evaporates as it dries, leaving behind the pigment, resin and additives that make up the paint. The last decade has seen a distinct push towards water-based paints, because the solvent-based paints are less environmentally-friendly. Solvents release Volatile Organic Compounds as they dry, hazardous chemicals which can not only damage health, but also contribute to smog formation.