How do I set up and use the Toss app in Korea?

Toss is an all-in-one finance app for transfers, viewing all your accounts and cards in one place, paying bills, splitting payments, and checking your credit score, and it even has its own Toss Bank account and card. Foreigners with an ARC, a Korean bank account, and a Korean phone number can sign up, with identity verification done through your phone. It's especially handy for free transfers and tracking your spending.