There are many forms of card advantage in the game of yugioh. Having any will, supposedly, help you. That is, if you think in advantage.
There is hand advantage. More cards in your hand.
EG: Pot of Greed
There is Feild advantage. More cards on your feild
Life advantage: More life than the enemy.
EG: Des Koala, hidden Machine gun.
Then theres information advantage. More information about the enemy's deck.
EG: CCV, DDV, EEV.
Tempo Advantage. Where your faster than the enemy. Most applicable in early game.
EG: Kick Back, CED.
Graveyard Advantage. Where you have a better graveyard status than the enemy.
EG: Foolish for Mezuki, PSZ, Wulf, Malicious
Temporary Advantage: Like it says, temporary advantage.
EG: Reckless Greed
Summoning Advantage: One of my favorites. Summoning more in one turn the the opponent.
EG: Monster reborn, but also Ultimate offering.
Attack number advantage: The number of attacks in one turn.
EG: Assault Armor
Mental Advantage: Having a feeling of equality over opponent. Not applicable if you are not mental.
EG: Yu-Jyou Friendship.
Confidence Advantage: Thinking, no... KNOWING your going to beat the opponent. More commonly known as "Arrogant Bastard Advantage"
EG: Using BF deck, Netdecking.
And that concludes our talk on various forms of advantage. I think most of us already know all of them.