Deck .................................................(40 to 60 cards)
Assemble your favorite cards into a Deck that follows these rules:
The Deck must be 40 to 60 cards.
You can only have up to 3 copies of the same card in your Deck,
Extra Deck and Side Deck combined.
Also, some cards are Forbidden, Limited or Semi-Limited in official
tournaments. http://www.yugioh-card.com/en/limited/
Try to keep your Deck close to the 40-card minimum. Having a Deck
with too many cards makes it hard to draw your best cards when you
need them. This Deck is called your Main Deck.

 Extra Deck............................................(0 to 15 cards)
This Deck consists of Xyz Monsters, Synchro Monsters and Fusion
Monsters, which can be used during the game if you meet certain
requirements. The rules for Extra Decks are:
You can have up to 15 cards in the Extra Deck.
The Extra Deck can only contain Xyz Monsters, Synchro Monsters
and Fusion Monsters.
These cards are not counted towards the 40-card minimum limit of
your Main Deck.

 Side Deck .............................................(0 to 15 cards)
This is a separate Deck of cards you can use to change your Deck
during a Match. After each Duel in a Match, you can swap any card
from your Side Deck with a card from your Deck and/or Extra Deck to
customize your strategy against your opponent. The number of cards in
your Side Decks must not exceed 15. The number of cards in your Side
Deck before and after you swap any cards must be exactly the same.

I think you should also mention about Pendulum monsters and how they can increase the extra deck's size in the duel.Just saying