it depends what year the action replay is
On an action replay, its program or ect.
it may damage your game and gameboy
You must have an Action Replay or Gameshark. For good Action Replay codes check the neoseeker website. :)
You need the action replay to activate the codes.
You enter them on Action Replay, then activate them.
You may only use gameshark for Pokemon firered codes! Buy the gameshark from gamestop. There are gameshark codes on youtube and supercheats.
If it is being transferred from an Action Replay DS to an Action Replay DSi, using the same version of the game, the same codes will work. I used to have both, and I find that my codes from Pokemon: Explorers of Time still works on my Action Replay DSi, even though I originally put them on my Action Replay. You just have to enter the code correctly, and know how to activate it (auto-activate, L+R, etc.). Then it will work.
you need the action replay devise and it should be self explanitory once you do. note: action replay and gameshark codes are different.
You need to hit (L+R)
There are codes already on Action Replay. What you have to do si insert your game in the Action Replay and the game should appear on the screen. When you get there, press the * button and all the codes will appear. Only activate a couple at a time or it will crash your game. To select a code, press the A button. There are codes on Action Replay when you first get it.
You need to use Action Replay DS, or a flashcart that supports Action Replay codes.
You cant yet! they just came out with the game and you expect that there can already be action replay codes! I dont even think that there are codes with HeartGold and SoulSilver yet!