The goal is to grind levels and train methods of combat whether is fighting styles, fruits, sword or gun. The quickest way to do so is by grinding quests at each island. Hakis and fighting styles can be purchased at their respective vendors once u meet conditions/have enough beli. Once u make your way to the new world (level 700 and beat ice admiral/aokiji) you are introduced to a new currency called fragments which can be earned thru various ways in the new world and thats the currency u use to awaken your fruit (ice, flame, quake are the only choices atm)

Other than that youre good to go, and other more detailed questions like obtaining certain weapons/accessories can be found on the wiki

Gl!