Commissions are paid out at the end of each month for sales that took place 3 months prior. For example, all commissions from February would be paid out on the last day of May. This window is to account for returns and processing. Keep in mind that this system means your first pay-out on Arthur will take place 3 months after your first sale occurred, at which point you'll continue to receive pay-outs at the end of each month assuming you made a sale 3 months prior.
Pay-outs are processed by the Arthur team, and are deposited into the bank account you connected to Stripe. You are required to connect a bank account to Stripe in order to receive pay-outs. To make sure you've set up your Stripe account, visit the billing page of your account.