Noob question pls help -,-

You can have one respec per difficulty by completing the Den of Evil quest from Akara in Act 1. These can be used at any time by starting a game in the appropriate difficulty: one in Normal, one in Nightmare and one in Hell.

Additionally, you can also create a Token of Absolution (this item allows a character infinite respecs) by transmuting the following items in your Horadric Cube:

1. Twisted Essence of Suffering from either Hell Andariel or Hell Duriel.
2. Charged Essence of Hate from Hell Mephisto
3. Burning Essence of Terror from Hell Diablo
4. Festering Essence of Destruction from Hell Baal