Template:Featured:Diablo 3 Basics
From Diablo Wiki
If you are new to Diablo III and want to get up to speed quickly but not ruin the game with spoilers then the Diablo 3 Basics article is the best place to start. It'll give you a run down of the different classes, items, npcs and gameplay systems that make up the game.
There are links throughout for further reading in you want to go into more depth.