Can someone explain to me in plain English how these cards work? I just bought my first commander deck and see all these cards that have no mana cost that I can see ( the test seems unclear to me) but I will put it on here so maybe someone can explain it.

Manifest: "You an cover a face down manifested creature with this reminder card. A manifested creature card can be turned face up any time for its mana cost. A face down card can be turned face up for its morph cost.

Another card is a Plant on one side and a Snake on the other, but there isn't any text except ''Token creature" on both sides. Is this different than a morph card? Should it be mixed in with the deck or kept on the side?

It doesn't specifically say any mana cost. What gives? I'm sort of new but not that new. I haven't played commander yet and there is about 10 of these kinds of cards mixed into the Faceless Menace deck that I bought today.

L

Those are play aids. The manifest aid is something you can use when you are instructed to manifest a card (like with Reality Shift). You could just not use the manifest play aid and just have the card face down and remember that it’s manifested, but the aid removes the need to add one more thing to remember in a busy game.

Similarly, the plant / snake token is a play aid you can put on the battlefield With the relevant face showing when Grismold or a Hooded Hydra tells you to create a plant token or a snake token. You can still do those things even if you don’t have that token play aid, and you can use anything to represent the created creature token. But that piece of cardboard helps, as above, at making the board state clear and obvious. You can use a Dorito to say “that dorito is a green 0/1 plant token creature”... or you can use a piece of cardboard that was made specifically to represent that information.

You don’t put them in your deck. You keep them with your deck out of convenience but you don’t shuffle them in. You just keep them nearby so that you have them when you want to use them to help you represent the game state.

I think I understand. There is about ten of these two sided cards and none of them have a mana cost as far as I can see so it’s a little confusing to me since I’m Just gettujg back into the game.

When I'm using Kadena (Black and green Legendary creature) and it says in the text "The first face down creature you cast each turn cost (3) less mana to cast" Is this referring to the two sided cards? I have I think 3 different types of double sided cards. Also, how does this work with one of the blue cards I have that does have a mana cost and says in the text that it can be cast face down as a 2/2 creature. Hopefully I'm being clear enough on this, I know it's kind of a lot, but I don't want to go to a tournament being the biggest newbie ever because then I'll be seen as easy pickings when playing in a free for all.

This is unrelated but in the commander deck I bought there is 230 cards total including the two sided cards and lands. I thought it might bd a sideboard but there’s too many for that. is WOTC giving me extra cards with the expectation that I’m going to tweak the deck a bit?

Can anyone help me understand this.?

Ignore the two-faced reminder "cards" for the time being.
They aren't game objects, they are just there to help you keep track of things. When you understand how the mechanics work, you will understand how to use them, but you don't actually have to use them.

https://mtg.gamepedia.com/Morph
https://mtg.gamepedia.com/Manifest

Kadena’s ability is strictly about those cards with morph. Cards with morph (or mega morph), you can ordinarily cast face down for 3 mana (then as a later play, turn them face up for their morph or mega morph cost). Kadena’s ability (if it’s on the battlefield), makes the first face down creature you cast per turn cost 3 less (since this cost is usually 3 this would reduce that 3 to 0 - effectively making your first facedown creature you cast each turn free).

There is no sideboard. There are exactly 100 magic cards in each commander deck - your commander and 99 other cards. And this is exactly how many cards are in the decks you buy in stores. The things you keep calling ‘cards’ that are tokens or manifest reminders - aren’t *cards*. They may be the same size and shape as cards but they’re not, in game terms, cards. They’re just helpful pieces of cardboard you keep around to help make the game state clear. But they aren’t cards. You have to learn to understand that. They don’t get shuffled in your deck. They will never be in your hand.

In your commander deck you bought in a store, the 100 pieces of cardboard that are the normal size and have the normal Magic: the Gathering back are your deck. Everything else is a play aid. Not a card.

You said 230 cards!? In one retail commander box? 230 wouldn’t even fit in one of those boxes. Did you typo? There’s typically about 110 pieces of cardboard in a commander product - 100 cards, one to three jumbo oversized representation(s) of that deck’s intended commander(s), and then a bunch of play aids.

All of that is correct.
Kadena's second ability also works on Manifest tho.