To better understand what happens during the projection process, imagine the earth as a large inflated balloon. Cut it apart, and flatten it to make a map. It will be stretched in some places, shrunk in others. Think of where and how the original balloon has been distorted. The equator is the longest parallel.
All meridians are of equal length.
Meridians converge at the poles. At a given latitude, meridians are equally spaced. Latitude and longitude meet at right angles. Note how areas are increasingly enlarged towards higher lattitudes. Map projections that do not fit within these three classes are described as Pseudo or Miscellaneous projections.