You should post a topic in Card Suggestions with the title being the card name if you're only posting one card (and whatever you want if more than one). Each card should have the fields described in the template below depending on what type of card it is. Make sure to type grammatically, or there's a much lower chance anyone will look at your cards.
Also, it's not recommended that you submit cards unless you've dueled with many of the cards in CLTCG and know how to create balanced cards. However, if you think you're an exception to that rule, you probably are.
Effect (What happens when you play it? Remember, after this happens, the card is sent to the void, so you can't, for example, say "You can use this card 5 times.")
Effects (These are usually activated effects, i.e. when the card is in play a player activates them. Specify how many times these effects can be used. It's also possible to specify constant powers, i.e. Gain +1 to all attacks)
Life Points (How many max life points?)
Attack (How many life points can this card attack for each turn?)
Effects (These should be constant effects that apply to both players, i.e. Both duelists gain +1 to all attacks. It is possible to specify these attacks as activated, i.e. Each duelist may once per game do ... but that is probably a bad idea.)
(Optional) Card Image (This really isn't required, but either a description of a image from Code Lyoko or a link to an image is helpful.)