Dragonball is the precursor to Dragonball Z. Where in DBZ Son Goku is an adult with a child of his own, Dragonball is the story of Goku's own youth, the beginning of it all.

This includes his meeting Bulma, his family history, his training alongside Kururin(or Krillin) under the Turtle Master, and the beginning of his quest for the Dragonballs. Among other things.

Dragonball has a significantly different style than Dragonball Z: it is humorous and fun, with relatively little fighting. It is also filled with perverted jokes, although DBZ might have had the same before it was translated into a kid's show.

All I know of the original Dragonball is from the manga, I have heard that although there is a single movie which covers all of Dragonball, that it is horrendous in every way imaginable.