As ShadowTiger explained quite well LTTP, it was much more than a tiny mistake. You also need to listen when people, especially the host, tell you not to do certain things. If I let you back, we run the risk of you doing the same thing again, and thus disrupting the gameplay experience for others again. While I do believe that you are sorry, I'm not sure if you completely understand what you did wrong. Otherwise, you wouldn't be referring to it as a "tiny" mistake. If you can prove that you fully understand why you were banned, then I might consider letting you rejoin us. I need to be confident that history isn't going to repeat itself.
As for coolgamer's questions:
Steam is a place where you can purchase games and download them without the need to travel to a store (in the traditional sense), play them, communicate with other players, etc. It's really a whole lot of things in one. To play the PC version of Terraria, you do need steam. Steam itself is free to download. Just go here, and click install steam. Prices for games vary, depending on what the game is currently being sold for, for example, although there are a few free games that exist on Steam as well. $10 is the most Terraria has ever sold for (and usually sells for this price). Steam has its own online store where you can purchase a game, provided you have a credit card available for such a purpose. As for other forms of payment available, I don't have an answer to that. Once you purchase a game on your account, you are able to download it as often as you want. It's pretty easy once you have downloaded steam and see where the store is.

