What are checks?

The episode you’ve been waiting for is finally here. This is part 2 of the San Fran Fin Lit Pod Con cliffhanger episode from last season. Bridget and Ryan finally made it to the conference, only to find it’s entirely cashless. It’s the perfect opportunity to answer all your non-paper-money questions: What would happen if we lived in a cashless world and paid for everything with debit and credit cards? How do you send and receive money with mobile payment apps? And how exactly do checks work?