What is a side board in magic the gathering?

Question

I just started playing MTGO and don't know alot about it. My question right now is what is a sideboard, what is it used for, and how do you use it?

Answer 1

A sideboard is 15 cards that are not in the main deck. In a tournement, after the first game, you may change any number of cards in the main deck to the sideboard.

Answer 2

From Magic: The Gathering's Floor Rules:

122. Sideboard Use

If a player wishes to use a sideboard, it must contain exactly fifteen cards.

Before each game begins, players must present their sideboards and allow their opponents to count the number of cards in their sideboards (face down), if requested. Players may look at their sideboards during a game only if the sideboard remains distinguishable from other cards. If a player is resolving a spell or effect that refers to “choosing a card from outside the game,” the player may look at his or her sideboard. (See section 103). The sideboard must be clearly identified and separated from all other cards in the play area. The sideboard may not be kept where it could be confused or switched with other cards.

The deck and sideboard must each be returned to their original compositions before the first game of each match. Cards transferred from a player’s deck to his or her sideboard, and vice versa, must be

returned before the player begins a new match. If a penalty causes a player to forfeit the first game in a match before that game began, neither player may use cards from his or her sideboard for the second game.

Before the beginning of the second or subsequent game in a match, players may change the composition of their decks by exchanging cards from their decks for cards in their sideboards. Any card exchange between decks and sideboards must be made on a one-for-one basis to ensure that the sideboards remain at exactly fifteen cards. There are no restrictions on the number of cards a player may exchange this way. Players are not required to reveal how many cards he or she is sideboarding.

To sum up, a sideboard in a constructed match must either be 0 cards or 15 cards. When you use the sideboard, you must switch cards out on a 1 to 1 basis so you always have 15 cards in the sideboard.

Why would you want a sideboard? Say your deck does well against many other decks, but there are 1 or two deck types that you lose to. You have cards in your sideboard that would be useful to you in those matches and you switch out cards that are of no use to you for those matches.

Answer 3

A sideboard is a collection of 15 cards that you can use to subsitute in for cards in the main deck in order to "patch" weak spots in certain matchups for your deck.

For example, if I was playing a deck, and I know that I need that one card to deal with a certain other deck, and I happened to be  playing that deck, in game 2, I could "side in" that card and hopefully win the game.

Glad to see some new blood in MtG! Keep on playing!