How do you put the cheats in?

Through the Action Replay device. I've never actually used one, so I'm no expert at it. If you want some real help on it, some cheats for the Action Replay, or just someone to discuss it with you, you should make a thread in the Action Replay forum located here. The people there would be willing to answer any questions you have.

If you mean action replay which is a cheat device that you could buy in some electronic store, (it comes with a cable and a disc, but I've lost those so I have to enter codes manually and this is how I do it)it's a little difficult, Put it in your DS, and wait till, the menu is on, then take out the AR and put in your game. It should say UNKNOWN GAME on the top screen, and the bottom-left of the top screen, there's a code which is the game ID, this may vary depending on your country. Either remember that code, or look it up on the internet, press the star button, and it won't have any games. Click add game, right it's name (That's not essential) And enter the ID, then it will have that game's menu, with no cheats click add cheat, and enter the cheat code! Now whenever you want to ativate that cheat, put your action replay in, turn on Your DS put in that game (If it doesn't show the name you gave that game on the top screen, you entered the ID wrong) and click the star button. It will bring you straight to the cheats for said game, check that cheat code (press A when your cursor is on it) and click START on the lower screen. It will start the game with the cheat on. If it doesn't work, check the code, to see if you did it right or maybe the code is faulty or not for your version of the game. I know it's long and confusing but I hope I helped anyway!

Hey I have just a plain old ds with Pokemon heart gold I'm trying to get Mew I don't have an enternet is it possible to catch Mew without cheating or wifi or traiding can I catch Mew in heart gold