How to receive Gamestop/Toys R Us Events.

1) Go to your local Gamestop or Toys R Us, depending on where the event is held.

2) Go find the spot with the Pokémon Event Sign.

Spoiler:

^example from the Deoxys Event^

3) Make sure you have the pokédex in your game, if not get it.

4) Bring your Pokémon Diamond/Pearl/Platinum, location events are usually able for all 3 versions meaning you could have more than one.

5) Turn on your DS/DSi and select the Pokémon game.

6) BEFORE you continue your saved file, click "Mystery Gift".

7) Click "Receive Gift", "GET VIA WIRELESS", and "Yes". It will search for the Event, you should find it. If you do not, go talk to the workers of the store, they might not have set it up right.

Spoiler:

^example from Darkari Event that tells you how to do it^

8) Go to the nearest Poké Mart, find the delivery man inside(dressed in green). He will give you the event.

Monkey

If you need help understanding it, here is a video I saw ages ago about it. I DID NOT MAKE IT!!