Choose what kind of debt this is (loan, installment plan, credit card, personal debt, or other — this is just for your own organization), and give it a name. If it's helpful, add who you owe it to and a short description.
For the amount, you can either enter the total you'll repay directly, or break it down into a principal plus interest and fees and let the total be worked out for you — either way works, so use whichever makes more sense for how you think about the debt. Note that any interest rate you enter is just for your own reference; it won't change how the payments are actually split up.
Decide how many installments it should be split into and how often they're due — weekly, monthly, quarterly, or yearly — along with the date of the first payment. If you're entering a debt that's already partway paid off, there's a switch to mark the earlier installments as already settled, without creating any transactions for them.
Finally, if you want payments to move real money, link it to an account. You can also assign a category so every generated payment is sorted consistently, and set how many days ahead of time you'd like a reminder.