Getting a game started
Create a game and you get a six-character code. Send it to whoever you want playing. They open bad.cards in a browser, type the code, and they are in. Only the person starting the game needs an account, so nobody has to sign up on your behalf while everyone waits.
A round, in order
The judge for the round sees a prompt with a blank in it. Everyone else picks a card from their hand to fill that blank, and plays it face down. Once everyone has answered, the cards flip, somebody reads them out, and the judge picks a winner. That player takes the point, everyone draws a new card, and the judge passes to the next person.
Winning
You set the number of rounds when you create the game. Most groups play eight to ten, which lands around fifteen minutes. Highest score at the end wins, and the game tells you who that is so nobody has to keep count.
Choosing packs, and how far it goes
Before the first round you pick which card packs are in play and set a content rating. That rating is the ceiling for the whole game, so it is the thing to get right if you have a mixed group. You can change both between games.
Other ways to play
Standard is one prompt and one judge. There are also modes where you type your own answer instead of playing a card, where answers are images, and where everyone picks a top three rather than one person deciding. Same group, genuinely different game.