Most yarns that you will find at the big craft store chains or at discount stores that sell yarn comes either in a ball or a skein. A ball is literally a round conglomeration of yarn. The yarn can be pulled from the outside of the ball, and sometimes from the inside as well.
A skein is similar to a ball but it is formed into an oblong shape. Its the classic shape most people think of when they think of yarn. Yarn can be pulled either from the outside or the inside of a skein of yarn.
A hank is a different way of selling yarn in which the yarn is loosely wound into a large ring shape and then twisted on itself to make a package thats easy to ship and store. Untwist the hank and youll find yourself faced with a big ring of yarn that needs to be wound into a ball before it is used.
Hanks, balls and skeins are all fine to work with; one is not a better choice than the others. Many luxury yarns and high-quality yarns are only available in hanks, so youll have to work with one sooner or later.