Are you wanting to play the cards against humanity for the first time or many you just want to know How many cards do you start with in Cards Against Humanity.
All players start with 10 white cards, after the card czar ( game judge) picks the winning white in each round player needing more white cards can draw another 10 cards. But all players should only hold a maximum of 10 white cards at any time throughout the game.
All player start with 10 white cards, the 10 white answer cards you are holding are the only card you have unit the end of the round. The round end when the card czar pick the winning answer the black question card.
All Basic Games of cards against humanity use the reboot the universe rule, which allows any player to draw another 10 white between the rounds.
Same alternative rules game of cards against humanity like the drinking game, the strip game, and the gambling game require to do something before you can draw more cards.