How does teetering peaks work in Magic the Gathering?

Arix is absolutely right, but he doesn't actually provide a direct answer, so I thought I'd chime in.

Teetering Peaks is a land card, which taps for red mana, just like a mountain. It is not a mountain, and it does not let you get a mountain (from your hand or otherwise), it just comes onto the battlefield itself as your land-drop for that turn.

This means that your Plated Geopede will get +2/+0 for the Teetering Peaks and +2/+2 for it's own Landfall ability triggering as Teetering Peaks enters the battlefield (it doesn't care whether the land is a Basic Land, such as a Mountain, or not). So yes, your Geopede will be a 5/3 (with First Strike, ouch).

Teetering Peaks enters the battlefield tapped, so you can't use it to pay for anything on the turn it enters the battlefield, but on every subsequent turn you can use it to make 1 red mana, just as you would a mountain.

You need to have the distinction between land and mana clear in your mind. I recommend reading section 106 and 305 (Mana and Land) of the comprehensive rulebook.

Teetering Peaks

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RE:

How does teetering peaks work in Magic the Gathering?

I know you dont search your deck out for a mountain card, but do you have to have a mountain in your hand to play it? so you can add that mountain to your mana pool? or can you just lay teetering peaks down in your mana pool and say it is a mountain? The reason i am confused is because, Geopede...

A common mistake among new players is confusing "land" with "mana" - they are not the same thing. Mana is an intangible "substance" that is produced by the physical land cards. That mana is then stored in your "mana pool", where it stays until either you spend it or the step ends. All Mountains have the ability "T: Add R to your mana pool", just like Teetering Peeks.

A good metaphor is that land is fruit and mana is juice. When you squeeze (tap) the fruit (land), you get juice (mana), not more fruit.

It's already been answered, but I think it might be helpful to add that your 'mana pool' and all the mana inside it is... intangible. It's imaginary. Adding mana to it or paying for spells by removing it is all something you keep track of mentally.